Update CHANGELOG.md

Author: cristianoc

CHANGELOG.md

@@ -52,6 +52,7 @@
 - Improve output of record copying. https://github.com/rescript-lang/rescript-compiler/pull/7043
 - Provide additional context in error message when `unit` is expected. https://github.com/rescript-lang/rescript-compiler/pull/7045
 - Improve error message when passing an object where a record is expected. https://github.com/rescript-lang/rescript-compiler/pull/7101
+- Improve code generation or pattern matching of untagged variants. https://github.com/rescript-lang/rescript-compiler/pull/7128
 
 #### :house: Internal