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

tests/handlers/test_profile.py

@@ -208,7 +208,9 @@ class ProfileTestCase(unittest.HomeserverTestCase):
         # Set avatar to an empty string
         self.get_success(
             self.handler.set_avatar_url(
-                self.frank, synapse.types.create_requester(self.frank), "",
+                self.frank,
+                synapse.types.create_requester(self.frank),
+                "",
             )
         )