clear and repeatable unreferenced license file detection

Observationally currently it can be unclear (i.e. warning but not failing) and inconsistent in repeat runs (more detections on second run) e.g. https://lists.apache.org/thread/hlh1bmtgnmp55q8knhjtltf8t57pbl5q and https://github.com/apache/solr/pull/2178#issuecomment-1917513343 reports.