`Plugin output is unparseable` when running protoc with google-api-core 2.28.0 and newer

[parthea]

See this build log which shows the error Plugin output is unparseable.

The error only appears in google-api-core 2.28.0 and newer when running with Python < 3.11. The error appears to be caused by the warnings that are emitted from google-api-core.

[parthea]

Transferring to google-cloud-python as the code for gapic-generator will be migrated there.