Bump google-cloud-firestore from 2.19.0 to 2.20.0 (#86)

Bumps [google-cloud-firestore](https://github.com/googleapis/python-firestore) from 2.19.0 to 2.20.0.
- [Release notes](https://github.com/googleapis/python-firestore/releases)
- [Changelog](https://github.com/googleapis/python-firestore/blob/main/CHANGELOG.md)
- [Commits](googleapis/python-firestore@v2.19.0...v2.20.0)

---
updated-dependencies:
- dependency-name: google-cloud-firestore
  dependency-type: indirect
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>