Fix owner warning when importing FBX.

modules/fbx/fbx_document.cpp

@@ -2017,6 +2017,7 @@ void FBXDocument::_process_mesh_instances(Ref<FBXState> p_state, Node *p_scene_r
 		ERR_CONTINUE_MSG(skeleton == nullptr, vformat("Unable to find Skeleton for node %d skin %d", node_i, skin_i));
 
 		mi->get_parent()->remove_child(mi);
+		mi->set_owner(nullptr);
 		skeleton->add_child(mi, true);
 		mi->set_owner(skeleton->get_owner());