build(deps): bump @google-cloud/firestore from 4.12.2 to 4.13.1 (#1369)

Bumps [@google-cloud/firestore](https://github.com/googleapis/nodejs-firestore) from 4.12.2 to 4.13.1.
- [Release notes](https://github.com/googleapis/nodejs-firestore/releases)
- [Changelog](https://github.com/googleapis/nodejs-firestore/blob/master/CHANGELOG.md)
- [Commits](googleapis/nodejs-firestore@v4.12.2...v4.13.1)

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

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