Update tests to mock stderr from run_proc_async

tests/test_webservice.py

@@ -230,7 +230,7 @@ async def test_run_action(mode, cmd, retcode, expected, monkeypatch):
     job_db = mock.Mock()
 
     async def mock_run_proc_async(*args):
-        return retcode, b'Submitted job: 42'
+        return retcode, b'Submitted job: 42', b''
 
     monkeypatch.setattr(
         webservice.webservice, 'run_proc_async', mock_run_proc_async