Bump pub to b9afe9270c24d040b8ae465b4b37ba4f7f4b4cc5

Changes:
```
> git log --format="%C(auto) %h %s" 817e61d..b9afe92
 https://dart.googlesource.com/pub.git/+/b9afe927 Completely switch from pub.dartlang.org to pub.dev (#3611)
 https://dart.googlesource.com/pub.git/+/7b65fa73 update docs for running 'pub token' (#3602)
 https://dart.googlesource.com/pub.git/+/4c9ebd0e Content hashing of archives (#3482)

```

Diff: https://dart.googlesource.com/pub.git/+/817e61d9eb174f77dfd2cb1d1de45826f66ac6bf~..b9afe9270c24d040b8ae465b4b37ba4f7f4b4cc5/
Change-Id: I6d827dd64f822e0194e0e17e95a47f02b744b561
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/264701
Commit-Queue: Sigurd Meldgaard <sigurdm@google.com>
Reviewed-by: Jonas Jensen <jonasfj@google.com>

CHANGELOG.md

@@ -158,8 +158,16 @@ Updated the Linter to `1.28.0`, which includes changes that
 
 - Treats packages with sdk constraint lower bound `>=2.12.0` or more and upper
   bound `<3.0.0` as compatible with `<4.0.0`.
+- Introduces content-hashes in pubspec.lock, to protect against corrupted
+  package repositories.
+
+  These will show up in the lock file on the first run of `dart pub get`.
+
+  See https://dart.dev/go/content-hashes for more details.
 - Remove remaining support for `.packages` files. The flag
   `--legacy-packages-file` is no longer supported.
+- The client will now default to the `pub.dev` repository instead of `pub.dartlang.org`.
+  This will cause a change in pubspec.lock.
 - Support a new field [`funding`](https://dart.dev/tools/pub/pubspec#funding) in pubspec.yaml.
 - Validate the CRC32c checksum of downloaded archives and retry on failure.
 - `dart pub add foo:<constraint>` with an existing dependency will now update

DEPS

@@ -150,7 +150,7 @@ vars = {
   "ply_rev": "604b32590ffad5cbb82e4afef1d305512d06ae93",
   "pool_rev": "fa84ddd0e39f45bf3f09dcc5d6b9fbdda7820fef",
   "protobuf_rev": "1d175bef6043bc4bdef5970f6dbd6d3001124373",
-  "pub_rev": "817e61d9eb174f77dfd2cb1d1de45826f66ac6bf", # manually rev'd
+  "pub_rev": "b9afe9270c24d040b8ae465b4b37ba4f7f4b4cc5", # manually rev'd
   "pub_semver_rev": "7671359982b4be9bdf87e621dd1bcdeac242b4b9",
   "root_certificates_rev": "692f6d6488af68e0121317a9c2c9eb393eb0ee50",
   "shelf_rev": "39d820d4e32fc99c65f562786097487d597dcee1",