build(deps): bump @google-cloud/firestore from 6.4.2 to 6.4.3 (#2079)

Bumps [@google-cloud/firestore](https://github.com/googleapis/nodejs-firestore) from 6.4.2 to 6.4.3.
- [Release notes](https://github.com/googleapis/nodejs-firestore/releases)
- [Changelog](https://github.com/googleapis/nodejs-firestore/blob/main/CHANGELOG.md)
- [Commits](googleapis/nodejs-firestore@v6.4.2...v6.4.3)

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

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>