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/test_server.py

@@ -166,7 +166,10 @@ class JsonResourceTests(unittest.TestCase):
 
         res = JsonResource(self.homeserver)
         res.register_paths(
-            "GET", [re.compile("^/_matrix/foo$")], _callback, "test_servlet",
+            "GET",
+            [re.compile("^/_matrix/foo$")],
+            _callback,
+            "test_servlet",
         )
 
         # The path was registered as GET, but this is a HEAD request.