Bump google-auth from 2.13.0 to 2.28.1

Bumps [google-auth](https://github.com/googleapis/google-auth-library-python) from 2.13.0 to 2.28.1.
- [Release notes](https://github.com/googleapis/google-auth-library-python/releases)
- [Changelog](https://github.com/googleapis/google-auth-library-python/blob/main/CHANGELOG.md)
- [Commits](https://github.com/googleapis/google-auth-library-python/compare/v2.13.0...v2.28.1)

---
updated-dependencies:
- dependency-name: google-auth
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

requirements.txt

@@ -11,7 +11,7 @@ feedparser==6.0.8
 gitdb==4.0.9
 GitPython==3.1.41
 google-api-core==2.10.2
-google-auth==2.13.0
+google-auth==2.28.1
 google-cloud-core==2.3.2
 google-cloud-datastore==2.9.0
 google-cloud-storage==2.5.0