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/handlers/pagination.py

@@ -197,7 +197,8 @@ class PaginationHandler:
             stream_ordering = await self.store.find_first_stream_ordering_after_ts(ts)
 
             r = await self.store.get_room_event_before_stream_ordering(
-                room_id, stream_ordering,
+                room_id,
+                stream_ordering,
             )
             if not r:
                 logger.warning(
@@ -223,7 +224,12 @@ class PaginationHandler:
             # the background so that it's not blocking any other operation apart from
             # other purges in the same room.
             run_as_background_process(
-                "_purge_history", self._purge_history, purge_id, room_id, token, True,
+                "_purge_history",
+                self._purge_history,
+                purge_id,
+                room_id,
+                token,
+                True,
             )
 
     def start_purge_history(
@@ -389,7 +395,9 @@ class PaginationHandler:
                         )
 
                 await self.hs.get_federation_handler().maybe_backfill(
-                    room_id, curr_topo, limit=pagin_config.limit,
+                    room_id,
+                    curr_topo,
+                    limit=pagin_config.limit,
                 )
 
             to_room_key = None