Allow asyncio-waitpid threads in test cleanup check (#183831)

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

tests/conftest.py

@@ -472,7 +472,7 @@ def verify_cleanup(
     for thread in threads:
         assert (
             isinstance(thread, threading._DummyThread)
-            or thread.name.startswith("waitpid-")
+            or thread.name.startswith("asyncio-waitpid-")
             or "_run_safe_shutdown_loop" in thread.name
         )