Bump google-auth-oauthlib from 0.4.6 to 0.5.1

Bumps [google-auth-oauthlib](https://github.com/GoogleCloudPlatform/google-auth-library-python-oauthlib) from 0.4.6 to 0.5.1.
- [Release notes](https://github.com/GoogleCloudPlatform/google-auth-library-python-oauthlib/releases)
- [Changelog](https://github.com/googleapis/google-auth-library-python-oauthlib/blob/main/CHANGELOG.md)
- [Commits](googleapis/google-auth-library-python-oauthlib@v0.4.6...v0.5.1)

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

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

requirements.txt

@@ -47,7 +47,7 @@ gast==0.5.3
 gitdb==4.0.9
 GitPython==3.1.27
 google-auth==2.6.2
-google-auth-oauthlib==0.4.6
+google-auth-oauthlib==0.5.1
 google-pasta==0.2.0
 graphviz==0.19.1
 grpcio==1.44.0