use correct heading level for v4.0.15

Author: RobinMalfait

CHANGELOG.md

@@ -36,7 +36,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add missing suggestions when `--spacing(--value(integer, number))` is used ([#17308](https://github.com/tailwindlabs/tailwindcss/pull/17308))
 - Add `::-webkit-details-marker` pseudo to `marker` variant ([#17362](https://github.com/tailwindlabs/tailwindcss/pull/17362))
 
-### [4.0.15] - 2025-03-20
+## [4.0.15] - 2025-03-20
 
 ### Fixed