Update changelog

Author: thecrypticace

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Types: allow for arbitrary theme values (for 3rd party plugins) ([#7926](https://github.com/tailwindlabs/tailwindcss/pull/7926))
 - Don’t split vars with numbers in them inside arbitrary values ([#8091](https://github.com/tailwindlabs/tailwindcss/pull/8091))
+- Require matching prefix when detecting negatives ([#8121](https://github.com/tailwindlabs/tailwindcss/pull/8121))
 
 ### Added