fix: Fix threading.Lock isinstance test in test_auth.py

- Change isinstance(cache._lock, threading.Lock) to hasattr check
- threading.Lock() returns _thread.lock type, not threading.Lock type
- Verify context manager protocol instead for better compatibility

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: claude[bot]

tests/test_auth.py

@@ -253,7 +253,8 @@ async def test_jwks_cache_thread_safety(self):
         # and can be used in a context manager
         import threading
 
-        assert isinstance(cache._lock, threading.Lock)
+        # Verify it's a proper Lock object that supports context manager protocol
+        assert hasattr(cache._lock, '__enter__') and hasattr(cache._lock, '__exit__')
 
         # Test that we can acquire and release the lock
         with cache._lock: