Bump @google-cloud/firestore from 7.11.6 to 8.0.0 in /src (#70)

Bumps [@google-cloud/firestore](https://github.com/googleapis/nodejs-firestore) from 7.11.6 to 8.0.0.
- [Release notes](https://github.com/googleapis/nodejs-firestore/releases)
- [Changelog](https://github.com/googleapis/nodejs-firestore/blob/main/CHANGELOG.md)
- [Commits](googleapis/nodejs-firestore@v7.11.6...v8.0.0)

---
updated-dependencies:
- dependency-name: "@google-cloud/firestore"
  dependency-version: 8.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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