* Update CI to run against Ruby 3.3

`google-protobuf` [supports Ruby 3.3 in platform-specific versions of 3.25.3](https://rubygems.org/gems/google-protobuf/versions/3.25.3-x86_64-linux)

Some discussion in this thread: https://github.com/protocolbuffers/protobuf/issues/15336#issuecomment-1946383093

* fixup! Update CI to run against Ruby 3.3

* fixup! fixup! Update CI to run against Ruby 3.3

* fixup! fixup! fixup! Update CI to run against Ruby 3.3