chore: make library generation IT non-required (googleapis#3477)

In this PR:
- Make the library generation integration test non-required.

This integration test will be removed in googleapis#3476 because we will use cloud
build to run integration tests.

.github/sync-repo-settings.yaml

@@ -21,7 +21,6 @@ branchProtectionRules:
   - graalvm-presubmit-sdk-platform-java-a-downstream-kmsinventory (java-graalvm-ci-prod)
   - graalvm-presubmit-sdk-platform-java-b-downstream-kmsinventory (java-graalvm-ci-prod)
   - library_generation
-  - library-generation-integration-tests
   - library-generation-lint-python
   - library-generation-lint-shell
   - library-generation-unit-tests