Fix test_submit_cancel_future_expects_engine_cancellation_rpc_call for Python 3.13.12 (#7879)

Problem:
`test_submit_cancel_future_expects_engine_cancellation_rpc_call` started
failing in Python 3.13.12 whilst passing in 3.13.11. It seems the tested
future
is canceled before starting and so it cannot change the tested values.

Solution: Add a short sleep time so the future thread gets to run.

Author: pavoljuhas

cirq-google/cirq_google/engine/stream_manager_test.py

@@ -319,6 +319,7 @@ def test_submit_cancel_future_expects_engine_cancellation_rpc_call(self, client_
         async def test():
             async with duet.timeout_scope(5):
                 result_future = manager.submit(REQUEST_PROJECT_NAME, REQUEST_PROGRAM, REQUEST_JOB0)
+                await duet.sleep(0.001)  # Let result_future start before it is canceled
                 result_future.cancel()
                 await duet.sleep(1)  # Let cancellation complete asynchronously
                 manager.stop()