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
`](80d6dc9783/docs/code_style.md)
 - Update `code_style.md` docs around installing black to use the correct version

synapse/state/v2.py

@@ -118,7 +118,11 @@ async def resolve_events_with_store(
         if event.room_id != room_id:
             raise Exception(
                 "Attempting to state-resolve for room %s with event %s which is in %s"
-                % (room_id, event.event_id, event.room_id,)
+                % (
+                    room_id,
+                    event.event_id,
+                    event.room_id,
+                )
             )
 
     full_conflicted_set = {eid for eid in full_conflicted_set if eid in event_map}