Bump protobuf from 4.21.9 to 4.21.12 (#472)

Bumps [protobuf](https://github.com/protocolbuffers/protobuf) from 4.21.9 to 4.21.12.
- [Release notes](https://github.com/protocolbuffers/protobuf/releases)
- [Changelog](https://github.com/protocolbuffers/protobuf/blob/main/generate_changelog.py)
- [Commits](https://github.com/protocolbuffers/protobuf/commits)

---
updated-dependencies:
- dependency-name: protobuf
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

test_requirements.txt

@@ -1,6 +1,6 @@
 # Requirements to run unit tests. Tests import from
 # generated code.
-protobuf==4.21.9
+protobuf==4.21.12
 pytest==7.2.1
 grpc-stubs==1.24.12
 grpcio-tools==1.51.1