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/storage/databases/main/registration.py

@@ -79,13 +79,16 @@ class RegistrationWorkerStore(CacheInvalidationWorkerStore):
         # call `find_max_generated_user_id_localpart` each time, which is
         # expensive if there are many entries.
         self._user_id_seq = build_sequence_generator(
-            database.engine, find_max_generated_user_id_localpart, "user_id_seq",
+            database.engine,
+            find_max_generated_user_id_localpart,
+            "user_id_seq",
         )
 
         self._account_validity = hs.config.account_validity
         if hs.config.run_background_tasks and self._account_validity.enabled:
             self._clock.call_later(
-                0.0, self._set_expiration_date_when_missing,
+                0.0,
+                self._set_expiration_date_when_missing,
             )
 
         # Create a background job for culling expired 3PID validity tokens