Retry cirq_google tests that have flaky CI failures on TimeoutError

Some tests in cirq_google.engine.stream_manager_test have
non-reproducible TimeoutError failures on CI runners, which
go away on retry.  Here we retry them by default.

Fixes #6741

cirq-google/cirq_google/engine/stream_manager_test.py

@@ -21,6 +21,7 @@
 import pytest
 import google.api_core.exceptions as google_exceptions
 
+import cirq
 from cirq_google.engine.asyncio_executor import AsyncioExecutor
 from cirq_google.engine.stream_manager import (
     _get_retry_request_or_raise,
@@ -368,6 +369,7 @@ async def test():
         ],
     )
     @mock.patch.object(quantum, 'QuantumEngineServiceAsyncClient', autospec=True)
+    @cirq.testing.retry_once_after_timeout
     def test_submit_with_retryable_stream_breakage_expects_get_result_request(
         self, client_constructor, error
     ):
@@ -407,6 +409,7 @@ async def test():
         ],
     )
     @mock.patch.object(quantum, 'QuantumEngineServiceAsyncClient', autospec=True)
+    @cirq.testing.retry_once_after_timeout
     def test_submit_with_non_retryable_stream_breakage_raises_error(
         self, client_constructor, error
     ):