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/identity.py

@@ -72,7 +72,10 @@ class IdentityHandler(BaseHandler):
         )
 
     def ratelimit_request_token_requests(
-        self, request: SynapseRequest, medium: str, address: str,
+        self,
+        request: SynapseRequest,
+        medium: str,
+        address: str,
     ):
         """Used to ratelimit requests to `/requestToken` by IP and address.