Use Protobuf 33.2 to generate code in google-cloud-ruby before Librarian migration

[suztomo]

In coming weeks, we'll onboard the libraries in google-cloud-ruby to Librarian, which uses protoc 33.2. The resulting migration pull request would have code diffs about the protoc timestamp documentation change because the timestamp classes come from protoc.

It would be ideal if the Ruby team uplift the google-cloud-ruby version to use protoc 33.2 with Bazel before Librarian migration. With this uplifting, the librarian migration pull requests are focused on the Librarian-related changes.

The protoc version for Bazel-based code generation is set at http://cs/google3/third_party/googleapis/stable/WORKSPACE;l=181 and is shared with other languages' code generation.

_protobuf_version = "31.0"

_protobuf_sha256 = "2b695cb1eaef8e173f884235ee6d55f57186e95d89ebb31361ee55cb5fd1b996"

http_archive(
    name = "com_google_protobuf",
    repo_mapping = {
        "@abseil-cpp": "@com_google_absl",
        "@protobuf_maven": "@maven",
    },
    sha256 = _protobuf_sha256,
    strip_prefix = "protobuf-%s" % _protobuf_version,
    urls = ["https://github.com/protocolbuffers/protobuf/archive/v%s.tar.gz" % _protobuf_version],
)

[suztomo]

@aandreassa I tentatively assigned you for this task. Please reassign it once your team decides who works on this.

[suztomo]

http://cs/google3/third_party/googleapis/stable/WORKSPACE;l=181

This is shared with the remaining languages in the Bazel project. In general upgrading something shared might not be trivial.

If this turned out to be difficult, alternatively, we can leverage Librarian's feature for languages to select protoc version independently (@JoeWang1127 implemented this). Ruby's Librarian onboarding can start with 31.0 to reduce the diff.