Tests should not automatically start failing when new year comes

[blakeli0]

See the issue in https://github.com/googleapis/sdk-platform-java/issues/3512 and the fix in https://github.com/googleapis/sdk-platform-java/pull/3513, all the golden tests started failing when 2025 came. This is due to the copyright year for GAPIC generated files are automatically set to current year. While this logic makes sense, we should have a way for the tests to not automatically failing when new year comes.

Potential solutions: Maybe add a conditional flag that is passed to all tests that if the generator knows it is running from a test, then the copyright year would be fixed.

[zhumin8]

fyi - same issue also exist in hermetic-build library-generation-unit-test, context: https://github.com/googleapis/sdk-platform-java/pull/3550