chore(deps): bump @google-cloud/firestore in /functions

Bumps [@google-cloud/firestore](https://github.com/googleapis/nodejs-firestore) from 5.0.1 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@v5.0.1...v6.2.0)

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

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Author: dependabot[bot]