chore(test): bump google-cloud-pubsub

Bumps [google-cloud-pubsub](https://github.com/googleapis/python-pubsub) from 2.21.2 to 2.21.3.
- [Release notes](https://github.com/googleapis/python-pubsub/releases)
- [Changelog](https://github.com/googleapis/python-pubsub/blob/main/CHANGELOG.md)
- [Commits](googleapis/python-pubsub@v2.21.2...v2.21.3)

---
updated-dependencies:
- dependency-name: google-cloud-pubsub
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/python-pubsub/requirements.txt

@@ -1,2 +1,2 @@
-google-cloud-pubsub==2.21.2
+google-cloud-pubsub==2.21.3
 avro==1.11.3