chore(deps): bump google-auth-httplib2 in /gmail/quickstart

Bumps [google-auth-httplib2](https://github.com/GoogleCloudPlatform/google-auth-library-python-httplib2) from 0.0.3 to 0.2.1.
- [Release notes](https://github.com/GoogleCloudPlatform/google-auth-library-python-httplib2/releases)
- [Changelog](https://github.com/googleapis/google-auth-library-python-httplib2/blob/main/CHANGELOG.md)
- [Commits](https://github.com/GoogleCloudPlatform/google-auth-library-python-httplib2/commits/v0.2.1)

---
updated-dependencies:
- dependency-name: google-auth-httplib2
  dependency-version: 0.2.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

gmail/quickstart/requirements.txt

@@ -1,3 +1,3 @@
 google-api-python-client==1.7.8
-google-auth-httplib2==0.0.3
+google-auth-httplib2==0.2.1
 google-auth-oauthlib==0.4.0