Update CHANGELOG.md

Author: jessevanassen

packages/scoped-custom-element-registry/CHANGELOG.md

@@ -6,6 +6,11 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 <!-- ## Unreleased -->
+## [Unreleased]
+
+### Fixed
+
+- `toggleAttribute` only triggers `attributeChangedCallback` when the attribute actually changes (#556).
 
 ## [0.0.9] - 2023-03-30