Bump google-auth-oauthlib from 1.3.1 to 1.4.0 (#7667)

Bumps [google-auth-oauthlib](https://github.com/googleapis/google-cloud-python) from 1.3.1 to 1.4.0.
- [Release notes](https://github.com/googleapis/google-cloud-python/releases)
- [Changelog](https://github.com/googleapis/google-cloud-python/blob/main/packages/gcp-sphinx-docfx-yaml/CHANGELOG.md)
- [Commits](https://github.com/googleapis/google-cloud-python/compare/google-auth-oauthlib-v1.3.1...google-auth-oauthlib-v1.4.0)

---
updated-dependencies:
- dependency-name: google-auth-oauthlib
  dependency-version: 1.4.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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