chore: [Backport] Add test for unregistering custom message handlers#3420

NoelStephensUnity merged 3 commits intodevelopUnity-Technologies/com.unity.netcode.gameobjects:developfrom

chore/mttb-1229/1.x/add-custom-messaging-unregister-testUnity-Technologies/com.unity.netcode.gameobjects:chore/mttb-1229/1.x/add-custom-messaging-unregister-testCopy head branch name to clipboard