Update changelog

Author: adamwathan

CHANGELOG.md

@@ -21,6 +21,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Only check selectors containing base apply candidates for circular dependencies ([#8222](https://github.com/tailwindlabs/tailwindcss/pull/8222))
 - Rewrite default class extractor ([#8204](https://github.com/tailwindlabs/tailwindcss/pull/8204))
 - Move `important` selector to the front when `@apply`-ing selector-modifying variants in custom utilities ([#8313](https://github.com/tailwindlabs/tailwindcss/pull/8313))
+- Error when registering an invalid custom variant ([#8345](https://github.com/tailwindlabs/tailwindcss/pull/8345))
 
 ### Changed