### 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_direction->draw_rect(Rect2(Vector2(), sun_direction->get_size()), Color(1, 1, 1, 1));
	Vector3 z_axis = preview_sun->get_transform().basis.get_column(Vector3::AXIS_Z);
	z_axis = get_editor_viewport(0)->camera->get_camera_transform().basis.xform_inv(z_axis);
	sun_direction_material->set_shader_parameter("sun_direction", Vector3(z_axis.x, -z_axis.y, z_axis.z));
	Color color = sun_color->get_pick_color() * sun_energy->get_value();
	sun_direction_material->set_shader_parameter("sun_color", Vector3(color.r, color.g, color.b));
}
void Node3DEditor::_preview_settings_changed() {