updating whatsnu

dist/preview release/what's new.md

@@ -24,6 +24,7 @@
 ### Core Engine
 
 - Fix ```shadowEnabled``` property on lights. Shadows are not visble anymore when disabled ([sebavan](http://www.github.com/sebavan))
+- Physics `unregisterOnPhysicsCollide` didn't remove callback correctly [#4291](https://github.com/BabylonJS/Babylon.js/issues/4291) ([RaananW](https://github.com/RaananW))
 
 ### Viewer