### 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)

_edit.mode = TRANSFORM_NONE;
	_edit.instant = false;
	_edit.numeric_input = 0;
	_edit.numeric_next_decimal = 0;
	_edit.numeric_negate = false;
	spatial_editor->set_local_coords_enabled(_edit.original_local);
	spatial_editor->update_transform_gizmo();
	surface->queue_redraw();
	set_process_input(false);
}
/
void Node3DEditorViewport::register_shortcut_action(const String &p_path, const String &p_name, Key p_keycode, bool p_physical) {
	Ref<Shortcut> sc = ED_SHORTCUT(p_path, p_name, p_keycode, p_physical);
	shortcut_changed_callback(sc, p_path);
	/
	sc->connect_changed(callable_mp(this, &Node3DEditorViewport::shortcut_changed_callback).bind(sc, p_path));
}
/
void Node3DEditorViewport::shortcut_changed_callback(const Ref<Shortcut> p_shortcut, const String &p_shortcut_path) {
	InputMap *im = InputMap::get_singleton();
	if (im->has_action(p_shortcut_path)) {
		im->action_erase_events(p_shortcut_path);
	} else {
		im->add_action(p_shortcut_path);
	}
	for (int i = 0; i < p_shortcut->get_events().size(); i++) {
		im->action_add_event(p_shortcut_path, p_shortcut->get_events()[i]);
	}
}
void Node3DEditorViewport::_set_lock_view_rotation(bool p_lock_rotation) {