[sdk-platform-java] [hermetic build] java-secretmanager v1beta1/clirr-ignored-differences.xml is not properly re-generated

java-secretmanager v1beta1/clirr-ignored-differences.xml is not properly re-generated
https://github.com/googleapis/google-cloud-java/blob/main/java-secretmanager/proto-google-cloud-secretmanager-v1beta1/clirr-ignored-differences.xml
Is empty.

Looks like this was introduced at re-generation: https://github.com/googleapis/google-cloud-java/pull/11402/changes

I believe `clirr-ignored-differences.xml` files are generated once and not overriden by hermetic build. This contradicts it.

Start with java-secretmanager v1beta1/clirr-ignored-differences.xml and compare its empty contents with the regeneration changes in pull request 11402. Trace how the hermetic build handles this generated file, then verify that regeneration produces the expected non-empty result without being overwritten.

Written by the indexing model from the issue text.