Update black, and run auto formatting over the codebase (#9381)

- Update black version to the latest
 - Run black auto formatting over the codebase
    - Run autoformatting according to [`docs/code_style.md
`](https://github.com/matrix-org/synapse/blob/80d6dc9783aa80886a133756028984dbf8920168/docs/code_style.md)
 - Update `code_style.md` docs around installing black to use the correct version

tests/module_api/test_api.py

@@ -100,7 +100,10 @@ class ModuleApiTestCase(HomeserverTestCase):
 
         # Check that the event was sent
         self.event_creation_handler.create_and_send_nonmember_event.assert_called_with(
-            expected_requester, event_dict, ratelimit=False, ignore_shadow_ban=True,
+            expected_requester,
+            event_dict,
+            ratelimit=False,
+            ignore_shadow_ban=True,
         )
 
         # Create and send a state event