- We don't recommend tox in `code_style.md`
- After #12107 it's much easier for black, isort and flake8 to find the
  scripts we want them to lint; we don't need to maintain `lint_targets`
  in the tox config. See also #12420.

The typechecking fix in #12389 only works if your local copy of
prometheus-client is at least version 0.14. Otherwise, it fails with:

    synapse/metrics/_types.py:22: error: Module "prometheus_client.registry" has no attribute "Collector"  [attr-defined]

Signed-off-by: Dan Callahan <danc@element.io>