generated client mypy issue

[daniel-sanche]

I'm seeing some mypy errors in #2085 that seem unrelated to the changes:

google/showcase_v1beta1/services/messaging/async_client.py:179: error: Argument 1 to "get_transport_class" of "MessagingClientMeta" has incompatible type "type[type[MessagingClient]]"; expected "MessagingClientMeta"  [arg-type]
google/showcase_v1beta1/services/identity/async_client.py:169: error: Argument 1 to "get_transport_class" of "IdentityClientMeta" has incompatible type "type[type[IdentityClient]]"; expected "IdentityClientMeta"  [arg-type]
google/showcase_v1beta1/services/echo/async_client.py:182: error: Argument 1 to "get_transport_class" of "EchoClientMeta" has incompatible type "type[type[EchoClient]]"; expected "EchoClientMeta"  [arg-type]
Found 3 errors in 3 files (checked 37 source files)

Separately, we noticed the same error message in python-datastore's gapic outputs, and resolved it by only type-checking veneer code

It seems related to this line in the gapic generator, which compiles to look like this. Maybe it should use {{ service.client_name }}Meta instead of type(self)?