update changelog

Author: RobinMalfait

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Allow using `@variant` with stacked variants (e.g. `@variant hover:focus { … }`) ([#19996](https://github.com/tailwindlabs/tailwindcss/pull/19996))
 - Allow using `@variant` with compound variants (e.g. `@variant hover, focus { … }`) ([#19996](https://github.com/tailwindlabs/tailwindcss/pull/19996))
 - Support `--default(…)` in `--value(…)` and `--modifier(…)` for functional `@utility` definitions ([#19989](https://github.com/tailwindlabs/tailwindcss/pull/19989))
+- Add `scrollbar-gutter-*` utilities ([#20018](https://github.com/tailwindlabs/tailwindcss/pull/20018))
 
 ### Fixed