update CHANGELOG

Author: EmandM

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -21,6 +21,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 
 ### Fixed
 
+- Fixed an exception being thrown when unregistering a custom message handler from within the registered callback. (#3417)
 - Fixed issue where the authority instance of NetworkTransform could check for state updates more than one time in a frame if the frame rate is greater than the tick frequency. (#3413)
 - Fixed issue where the new interpolator types were blocking after the first consumption of a sequence of buffered state updates. (#3413)
 - Fixed issue where root level in-scene placed `NetworkObject`s would only allow the ownership permission to be no less than distributable or sessionowner. (#3407)