### 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)

sun_environ_updating = true;
	/
	/
	/
	/
	/
	/
	sun_rotation = Vector2(-Math::deg_to_rad(60.0), Math::deg_to_rad(150.0));
	sun_angle_altitude->set_value(-Math::rad_to_deg(sun_rotation.x));
	sun_angle_azimuth->set_value(180.0 - Math::rad_to_deg(sun_rotation.y));
	sun_direction->queue_redraw();
	environ_sky_color->set_pick_color(Color(0.385, 0.454, 0.55));
	environ_ground_color->set_pick_color(Color(0.2, 0.169, 0.133));
	environ_energy->set_value(1.0);
	if (OS::get_singleton()->get_current_rendering_method() != "gl_compatibility") {
		environ_glow_button->set_pressed(true);
	}
	environ_tonemap_button->set_pressed(true);
	environ_ao_button->set_pressed(false);
	environ_gi_button->set_pressed(false);
	sun_max_distance->set_value(100);
	sun_color->set_pick_color(Color(1, 1, 1));
	sun_energy->set_value(1.0);
	sun_environ_updating = false;
}
void Node3DEditor::_update_preview_environment() {