Bump protobuf from 5.28.2 to 5.28.3 (#643)

Bumps [protobuf](https://github.com/protocolbuffers/protobuf) from 5.28.2 to 5.28.3.
- [Release notes](https://github.com/protocolbuffers/protobuf/releases)
- [Changelog](https://github.com/protocolbuffers/protobuf/blob/main/protobuf_release.bzl)
- [Commits](protocolbuffers/protobuf@v5.28.2...v5.28.3)

---
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==5.28.2
+protobuf==5.28.3
 pytest==8.3.3
 pytest-asyncio==0.24.0
 grpc-stubs==1.53.0.5