Update CHANGELOG.md

Author: keveleigh

org.mixedrealitytoolkit.uxcore/CHANGELOG.md

@@ -2,6 +2,12 @@
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
+## Unreleased
+
+### Fixed
+
+* Fixed build issue caused by `FontIconSelectorMigrationUtility` not being in an Editor-only assembly.
+
 ## [4.0.0-pre.3] - 2026-05-20
 
 ### Added