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/rest/key/v2/test_remote_key_resource.py

@@ -180,7 +180,8 @@ class EndToEndPerspectivesTests(BaseRemoteKeyResourceTestCase):
         async def post_json(destination, path, data):
             self.assertEqual(destination, self.hs.hostname)
             self.assertEqual(
-                path, "/_matrix/key/v2/query",
+                path,
+                "/_matrix/key/v2/query",
             )
 
             channel = FakeChannel(self.site, self.reactor)
@@ -188,7 +189,9 @@ class EndToEndPerspectivesTests(BaseRemoteKeyResourceTestCase):
             req.content = BytesIO(encode_canonical_json(data))
 
             req.requestReceived(
-                b"POST", path.encode("utf-8"), b"1.1",
+                b"POST",
+                path.encode("utf-8"),
+                b"1.1",
             )
             channel.await_result()
             self.assertEqual(channel.code, 200)