fix linting

Author: jooola

hcloud/actions/client.py

@@ -203,7 +203,7 @@ def wait_for_function(
 
         retries = 0
         wait = waiter(timeout)
-        while len(running):
+        while len(running) > 0:
             # pylint: disable=protected-access
             if wait(self._client._poll_interval_func(retries)):
                 raise ActionGroupException(