build(deps): bump protobufjs and google-gax

Bumps [protobufjs](https://github.com/protobufjs/protobuf.js) and [google-gax](https://github.com/googleapis/google-cloud-node-core/tree/HEAD/packages/gax). These dependencies needed to be updated together.

Updates `protobufjs` from 7.2.5 to 7.6.4
- [Release notes](https://github.com/protobufjs/protobuf.js/releases)
- [Changelog](https://github.com/protobufjs/protobuf.js/blob/protobufjs-v7.6.4/CHANGELOG.md)
- [Commits](protobufjs/protobuf.js@protobufjs-v7.2.5...protobufjs-v7.6.4)

Updates `google-gax` from 4.0.5 to 4.6.1
- [Release notes](https://github.com/googleapis/google-cloud-node-core/releases)
- [Changelog](https://github.com/googleapis/google-cloud-node-core/blob/main/packages/gax/CHANGELOG.md)
- [Commits](https://github.com/googleapis/google-cloud-node-core/commits/HEAD/packages/gax)

---
updated-dependencies:
- dependency-name: protobufjs
  dependency-version: 7.6.4
  dependency-type: indirect
- dependency-name: google-gax
  dependency-version: 4.6.1
  dependency-type: indirect
...

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Author: dependabot[bot]