build(deps): bump @google-cloud/firestore from 5.0.2 to 6.0.0

Bumps [@google-cloud/firestore](https://github.com/googleapis/nodejs-firestore) from 5.0.2 to 6.0.0.
- [Release notes](https://github.com/googleapis/nodejs-firestore/releases)
- [Changelog](https://github.com/googleapis/nodejs-firestore/blob/main/CHANGELOG.md)
- [Commits](googleapis/nodejs-firestore@v5.0.2...v6.0.0)

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

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

Author: dependabot[bot]