ruby: determine protoc v31.0 compatibility #4826
Description
We plan to use v31.0 for Go and Python (#4816) as they onboard to Librarian.
It would be useful to understand whether Ruby generation can work with protoc v31.0, and if not, what the specific constraints are.
The goal is to better understand the limitations and tradeoffs as we think about versioning more systematically in librarian. See #4815 for context.