✅(backends) fix test pollution caused by lrs backends cache

Clearing the cache after the loader test to ensure isolation and avoid
a test in `test_cli_usage` failing.

Author: wilbrdt

tests/backends/test_loader.py

@@ -200,3 +200,4 @@ def mock_entry_points(group):
         "fs": FSLRSBackend,
         "mongo": MongoLRSBackend,
     }
+    get_lrs_backends.cache_clear()