chore(deps): bump protobufjs and @google-cloud/firestore in /definitions

Bumps [protobufjs](https://github.com/protobufjs/protobuf.js) and [@google-cloud/firestore](https://github.com/googleapis/nodejs-firestore). These dependencies needed to be updated together.

Updates `protobufjs` from 6.11.3 to 7.2.4
- [Release notes](https://github.com/protobufjs/protobuf.js/releases)
- [Changelog](https://github.com/protobufjs/protobuf.js/blob/master/CHANGELOG.md)
- [Commits](protobufjs/protobuf.js@v6.11.3...protobufjs-v7.2.4)

Updates `@google-cloud/firestore` from 4.15.1 to 6.6.1
- [Release notes](https://github.com/googleapis/nodejs-firestore/releases)
- [Changelog](https://github.com/googleapis/nodejs-firestore/blob/main/CHANGELOG.md)
- [Commits](googleapis/nodejs-firestore@v4.15.1...v6.6.1)

---
updated-dependencies:
- dependency-name: protobufjs
  dependency-type: indirect
- dependency-name: "@google-cloud/firestore"
  dependency-type: indirect
...

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