test(aws): Fix aws trigger tests, use get_async_conn for mock object (apache#47667)

follow up of apache#47515

Author: Lee-W

providers/amazon/tests/unit/amazon/aws/triggers/test_mwaa.py

@@ -92,7 +92,7 @@ def test_serialization(self):
 
     @pytest.mark.asyncio
     @mock.patch.object(MwaaHook, "get_waiter")
-    @mock.patch.object(MwaaHook, "async_conn")
+    @mock.patch.object(MwaaHook, "get_async_conn")
     async def test_run_success(self, mock_async_conn, mock_get_waiter):
         mock_async_conn.__aenter__.return_value = mock.MagicMock()
         mock_get_waiter().wait = AsyncMock()