chore: Add volume mapping for testing with a SNAPSHOT version of gapi…

…c generator (#10954)

Add volume mapping for testing with a SNAPSHOT version of gapic generator.

This is a short term mitigation for testing google-cloud-java with a SNAPSHOT version of gapic generator. In long term, we should bake the generator into the docker images.

generation/hermetic_library_generation.sh

@@ -93,6 +93,7 @@ docker run \
   --rm \
   -u "$(id -u):$(id -g)" \
   -v "$(pwd):${workspace_name}" \
+  -v "$HOME"/.m2:/home/.m2 \
   gcr.io/cloud-devrel-public-resources/java-library-generation:"${image_tag}" \
   --baseline-generation-config-path="${workspace_name}/${baseline_generation_config}" \
   --current-generation-config-path="${workspace_name}/${generation_config}"