chore(deps): bump google-auth from 2.3.3 to 2.40.3 in /docs/mail-merge

Bumps [google-auth](https://github.com/googleapis/google-auth-library-python) from 2.3.3 to 2.40.3.
- [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](googleapis/google-auth-library-python@v2.3.3...v2.40.3)

---
updated-dependencies:
- dependency-name: google-auth
  dependency-version: 2.40.3
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

docs/mail-merge/requirements.txt

@@ -1,3 +1,3 @@
-google-auth==2.3.3
+google-auth==2.40.3
 google-api-python-client==2.31.0
 oauth2client==4.1.3