Fix TypeVar defaults with None (PEP 696)

[cdce8p]

Ref: #14851

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

steam.py (https://github.com/Gobot1234/steam.py)
- steam/badge.py:129: error: Argument 1 to "inventory" of "PartialUser" has incompatible type "tuple[str, int]"; expected "App[str]"  [arg-type]
+ steam/badge.py:129: error: Argument 1 to "inventory" of "PartialUser" has incompatible type "tuple[str, int]"; expected "App[str | None]"  [arg-type]
- steam/app.py:696: error: Argument 2 to "AppStats" has incompatible type "PartialApp[NameT]"; expected "App[str]"  [arg-type]
- steam/app.py:710: error: Argument 2 to "AppAchievement" has incompatible type "PartialApp[NameT]"; expected "PartialApp[str]"  [arg-type]
- steam/app.py:724: error: Type argument "Self" of "Leaderboard" must be a subtype of "App[str]"  [type-var]
- steam/app.py:736: error: Value of type variable "AppT" of "Leaderboard" cannot be "Self"  [type-var]
- steam/app.py:749: error: Type argument "Self" of "Leaderboard" must be a subtype of "App[str]"  [type-var]
- steam/app.py:765: error: Value of type variable "AppT" of "Leaderboard" cannot be "Self"  [type-var]
- steam/app.py:775: error: Type argument "Self" of "Leaderboard" must be a subtype of "App[str]"  [type-var]
- steam/app.py:786: error: Value of type variable "AppT" of "Leaderboard" cannot be "Self"  [type-var]
- steam/app.py:832: error: Argument 1 to "fetch_review" of "PartialUser" has incompatible type "PartialApp[NameT]"; expected "App[str]"  [arg-type]
- steam/app.py:1169: error: Type argument "Self" of "CommunityItem" must be a subtype of "PartialApp[str]"  [type-var]
- steam/app.py:1181: error: Value of type variable "AppT" of "CommunityItem" cannot be "Self"  [type-var]
- steam/app.py:1230: error: Type argument "Self" of "RewardItem" must be a subtype of "PartialApp[str]"  [type-var]
- steam/app.py:1240: error: Value of type variable "AppT" of "RewardItem" cannot be "Self"  [type-var]
- steam/app.py:1271: error: Value of type variable "AppT" of "AppBadge" cannot be "Self"  [type-var]
- steam/app.py:1300: error: Type argument "Self" of "RewardItem" must be a subtype of "PartialApp[str]"  [type-var]
- steam/app.py:1305: error: Type argument "Self" of "AppBadge" must be a subtype of "PartialApp[str]"  [type-var]
- steam/app.py:1316: error: Value of type variable "AppT" of "AppBadge" cannot be "Self"  [type-var]
- steam/app.py:1374: error: Argument 1 to "temporarily_play" of "ConnectionState" has incompatible type "PartialApp[NameT]"; expected "App[str]"  [arg-type]
- steam/profile.py:152: error: Argument 1 to "inventory" of "PartialUser" has incompatible type "tuple[str, int]"; expected "App[str]"  [arg-type]
+ steam/profile.py:152: error: Argument 1 to "inventory" of "PartialUser" has incompatible type "tuple[str, int]"; expected "App[str | None]"  [arg-type]
- steam/event.py:277: error: Incompatible types in assignment (expression has type "App[str] | PartialApp[str | None] | None", variable has type "PartialApp[str | None] | None")  [assignment]
+ steam/event.py:277: error: Incompatible types in assignment (expression has type "App[str | None] | None", variable has type "PartialApp[str | None] | None")  [assignment]
- steam/user_news.py:112: error: Argument 1 to "fetch_review" of "PartialUser" has incompatible type "PartialApp[str | None]"; expected "App[str]"  [arg-type]
- steam/ext/commands/commands.py:288: error: Incompatible types in assignment (expression has type "GroupMixin[Any] | Group[Any, [VarArg(Any), KwArg(Any)], Any] | None", variable has type "Self")  [assignment]
+ steam/ext/commands/commands.py:288: error: Incompatible types in assignment (expression has type "GroupMixin[Any | None] | Group[Any, [VarArg(Any), KwArg(Any)], Any] | None", variable has type "Self")  [assignment]
- steam/ext/csgo/models.py:179: note:          def inventory(self, app: App[str], *, context_id: int | None = ..., language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
+ steam/ext/csgo/models.py:179: note:          def inventory(self, app: App[str | None], *, context_id: int | None = ..., language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
- steam/ext/csgo/models.py:179: note:          def inventory(self, app: App[str], *, language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
+ steam/ext/csgo/models.py:179: note:          def inventory(self, app: App[str | None], *, language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
- steam/ext/csgo/models.py:179: note:          def inventory(self, App[str], /, *, context_id: int | None = ..., language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
+ steam/ext/csgo/models.py:179: note:          def inventory(self, App[str | None], /, *, context_id: int | None = ..., language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
- steam/ext/csgo/models.py:179: note:          def inventory(self, app: App[str], *, language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
+ steam/ext/csgo/models.py:179: note:          def inventory(self, app: App[str | None], *, language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
- steam/ext/csgo/models.py:179: note:          def inventory(self, App[str], /, *, context_id: int | None = ..., language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
+ steam/ext/csgo/models.py:179: note:          def inventory(self, App[str | None], /, *, context_id: int | None = ..., language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
- steam/ext/csgo/models.py:179: note:          def inventory(self, app: App[str], *, language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
+ steam/ext/csgo/models.py:179: note:          def inventory(self, app: App[str | None], *, language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
- steam/ext/tf2/client.py:36: note:          def inventory(self, app: App[str], *, context_id: int | None = ..., language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
+ steam/ext/tf2/client.py:36: note:          def inventory(self, app: App[str | None], *, context_id: int | None = ..., language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
- steam/ext/tf2/client.py:36: note:          def inventory(self, app: App[str], *, language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
+ steam/ext/tf2/client.py:36: note:          def inventory(self, app: App[str | None], *, language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
- steam/ext/tf2/client.py:36: note:          def inventory(self, App[str], /, *, context_id: int | None = ..., language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
+ steam/ext/tf2/client.py:36: note:          def inventory(self, App[str | None], /, *, context_id: int | None = ..., language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
- steam/ext/tf2/client.py:36: note:          def inventory(self, app: App[str], *, language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
+ steam/ext/tf2/client.py:36: note:          def inventory(self, app: App[str | None], *, language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
- steam/ext/tf2/client.py:36: note:          def inventory(self, App[str], /, *, context_id: int | None = ..., language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
+ steam/ext/tf2/client.py:36: note:          def inventory(self, App[str | None], /, *, context_id: int | None = ..., language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
- steam/ext/tf2/client.py:36: note:          def inventory(self, app: App[str], *, language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]
+ steam/ext/tf2/client.py:36: note:          def inventory(self, app: App[str | None], *, language: Language | None = ...) -> Coroutine[Any, Any, Inventory[Item[ClientUser], ClientUser]]