Bump protobufjs and google-gax in /functions (#587)

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

Updates `protobufjs` from 7.2.3 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@protobufjs-v7.2.3...protobufjs-v7.2.4)

Updates `google-gax` from 3.6.0 to 3.6.1
- [Release notes](https://github.com/googleapis/gax-nodejs/releases)
- [Changelog](https://github.com/googleapis/gax-nodejs/blob/main/CHANGELOG.md)
- [Commits](googleapis/gax-nodejs@v3.6.0...v3.6.1)

---
updated-dependencies:
- dependency-name: protobufjs
  dependency-type: indirect
- dependency-name: google-gax
  dependency-type: indirect
...

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Author: dependabot[bot]