Fix tests for 3.9

Author: puddly

tests/test_uart.py

@@ -139,7 +139,7 @@ async def mock_connect(loop, protocol_factory, *args, **kwargs):
 
 
 @pytest.fixture
-def gw():
+async def gw():
     gw = uart.Gateway(MagicMock())
     gw._transport = MagicMock()
     return gw