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/storage/test_background_update.py

@@ -67,7 +67,9 @@ class BackgroundUpdateTestCase(unittest.HomeserverTestCase):
         async def update(progress, count):
             self.assertEqual(progress, {"my_key": 2})
             self.assertAlmostEqual(
-                count, target_background_update_duration_ms / duration_ms, places=0,
+                count,
+                target_background_update_duration_ms / duration_ms,
+                places=0,
             )
             await self.updates._end_background_update("test_update")
             return count