RoughnessMipmapper: Restore fix for USDZExporter. (#22994)

examples/jsm/utils/RoughnessMipmapper.js

@@ -87,6 +87,7 @@ class RoughnessMipmapper {
 		material.roughnessMap.repeat.copy( roughnessMap.repeat );
 		material.roughnessMap.center.copy( roughnessMap.center );
 		material.roughnessMap.rotation = roughnessMap.rotation;
+		material.roughnessMap.image = roughnessMap.image; // required for USDZExporter, see #22741
 
 		material.roughnessMap.matrixAutoUpdate = roughnessMap.matrixAutoUpdate;
 		material.roughnessMap.matrix.copy( roughnessMap.matrix );