### 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)

real_t min_speed = MAX(camera->get_near() * 4, ZOOM_FREELOOK_MIN);
	real_t max_speed = MIN(camera->get_far() / 4, ZOOM_FREELOOK_MAX);
	if (unlikely(min_speed > max_speed)) {
		freelook_speed = (min_speed + max_speed) / 2;
	} else {
		freelook_speed = CLAMP(freelook_speed * scale, min_speed, max_speed);
	}
	zoom_indicator_delay = ZOOM_FREELOOK_INDICATOR_DELAY_S;
	surface->queue_redraw();
}
Point2i Node3DEditorViewport::_get_warped_mouse_motion(const Ref<InputEventMouseMotion> &p_ev_mouse_motion) const {
	Point2i relative;
	if (bool(EDITOR_GET("editors/3d/navigation/warped_mouse_panning"))) {
		relative = Input::get_singleton()->warp_mouse_motion(p_ev_mouse_motion, surface->get_global_rect());
	} else {
		relative = p_ev_mouse_motion->get_relative();
	}
	return relative;
}
void Node3DEditorViewport::_update_freelook(real_t delta) {