### Godot version

Master (4.2)

### System information

Windows 11 - Vulkan - Nvidia RTX 4070 - intel i5 13600KF

### Issue description

As you can see in the video when you try to add multiple scenes in to the 3D viewport (only with multiple scenes) the editor throws this error.

```
ERROR: Can't add child '@Node3D@18837' to '@SubViewport@9274', already has a parent '@SubViewport@9274'.
   at: (scene\main\node.cpp:1411)
```


Video: https://youtu.be/BVcCIigQJDw

This happens in the latest master (pulled on 2.11.2023).

### Steps to reproduce

Drag couple of the 3d mesh scenes into the 3D viewport and then select multiple scenes and drag them over and observer the error.

### Minimal reproduction project

[TestSceneDragAndDrop.zip](https://github.com/godotengine/godot/files/13253741/TestSceneDragAndDrop.zip)

do_snap_selected_nodes_to_floor = true;
}
void Node3DEditor::_snap_selected_nodes_to_floor() {
	const List<Node *> &selection = editor_selection->get_selected_node_list();
	Dictionary snap_data;
	for (Node *E : selection) {
		Node3D *sp = Object::cast_to<Node3D>(E);
		if (sp) {
			Vector3 from;
			Vector3 position_offset;
			/
			HashSet<VisualInstance3D *> vi = _get_child_nodes<VisualInstance3D>(sp);
			HashSet<CollisionShape3D *> cs = _get_child_nodes<CollisionShape3D>(sp);
			bool found_valid_shape = false;
			if (cs.size()) {
				AABB aabb;
				HashSet<CollisionShape3D *>::Iterator I = cs.begin();
				if ((*I)->get_shape().is_valid()) {
					CollisionShape3D *collision_shape = *cs.begin();
					aabb = collision_shape->get_global_transform().xform(collision_shape->get_shape()->get_debug_mesh()->get_aabb());
					found_valid_shape = true;
				}
				for (++I; I; ++I) {