Add PR number to CHANGELOG entry

Author: simon-lemay-unity

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -16,7 +16,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 
 ### Fixed
 
-- Fixed an issue in `UnityTransport` where the transport would accept sends on invalid connections, leading to a useless memory allocation and confusing error message.
+- Fixed an issue in `UnityTransport` where the transport would accept sends on invalid connections, leading to a useless memory allocation and confusing error message. (#3383)
 - Fixed initial `NetworkTransform` spawn, ensure it uses world space. (#3361)
 - Fixed issue where `AnticipatedNetworkVariable` previous value returned by `AnticipatedNetworkVariable.OnAuthoritativeValueChanged` is updated correctly on the non-authoritative side. (#3322)