Tell Black to format code for Python 3.5 (#8664)

This allows trailing commas in multi-line arg lists.

Minor, but we might as well keep our formatting current with regard to
our minimum supported Python version.

Signed-off-by: Dan Callahan <danc@element.io>

tests/replication/tcp/streams/test_events.py

@@ -449,7 +449,7 @@ class EventsStreamTestCase(BaseStreamTestCase):
                 sender=sender,
                 type="test_event",
                 content={"body": body},
-                **kwargs
+                **kwargs,
             )
         )