## Summary
Stabilizes C420 for the 0.10 release.
## Test Plan
No open issues or PRs (except a general issue about [string
normalization](https://github.com/astral-sh/ruff/issues/16579)). The
last (and only) false-negative bug fix was over a month ago.
The tests for this rule were already not on the `preview_rules` test, so
I just changed the `RuleGroup`. The documentation looked okay to me.
ed4152dec6