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
`](https://github.com/matrix-org/synapse/blob/80d6dc9783aa80886a133756028984dbf8920168/docs/code_style.md)
 - Update `code_style.md` docs around installing black to use the correct version

synapse/util/patch_inline_callbacks.py

@@ -204,16 +204,13 @@ def _check_yield_points(f: Callable, changes: List[str]):
                 # We don't raise here as its perfectly valid for contexts to
                 # change in a function, as long as it sets the correct context
                 # on resolving (which is checked separately).
-                err = (
-                    "%s changed context from %s to %s, happened between lines %d and %d in %s"
-                    % (
-                        frame.f_code.co_name,
-                        expected_context,
-                        current_context(),
-                        last_yield_line_no,
-                        frame.f_lineno,
-                        frame.f_code.co_filename,
-                    )
+                err = "%s changed context from %s to %s, happened between lines %d and %d in %s" % (
+                    frame.f_code.co_name,
+                    expected_context,
+                    current_context(),
+                    last_yield_line_no,
+                    frame.f_lineno,
+                    frame.f_code.co_filename,
                 )
                 changes.append(err)