Bump @google-cloud/firestore in /final-state/functions

Bumps [@google-cloud/firestore](https://github.com/googleapis/nodejs-firestore) from 4.7.1 to 6.2.0.
- [Release notes](https://github.com/googleapis/nodejs-firestore/releases)
- [Changelog](https://github.com/googleapis/nodejs-firestore/blob/main/CHANGELOG.md)
- [Commits](googleapis/nodejs-firestore@v4.7.1...v6.2.0)

---
updated-dependencies:
- dependency-name: "@google-cloud/firestore"
  dependency-type: direct:development
...

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

Author: dependabot[bot]