### 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)

}
		if (ED_IS_SHORTCUT("spatial_editor/orbit_view_down", p_event)) {
			
			cursor.x_rot = CLAMP(cursor.x_rot - Math_PI / 12.0, -1.57, 1.57);
			view_type = VIEW_TYPE_USER;
			_update_name();
		}
		if (ED_IS_SHORTCUT("spatial_editor/orbit_view_up", p_event)) {
			
			cursor.x_rot = CLAMP(cursor.x_rot + Math_PI / 12.0, -1.57, 1.57);
			view_type = VIEW_TYPE_USER;
			_update_name();
		}
		if (ED_IS_SHORTCUT("spatial_editor/orbit_view_right", p_event)) {
			cursor.y_rot -= Math_PI / 12.0;
			view_type = VIEW_TYPE_USER;
			_update_name();
		}
		if (ED_IS_SHORTCUT("spatial_editor/orbit_view_left", p_event)) {
			cursor.y_rot += Math_PI / 12.0;
			view_type = VIEW_TYPE_USER;
			_update_name();
		}
		if (ED_IS_SHORTCUT("spatial_editor/orbit_view_180", p_event)) {
			cursor.y_rot += Math_PI;
			view_type = VIEW_TYPE_USER;
			_update_name();
		}
		if (ED_IS_SHORTCUT("spatial_editor/focus_origin", p_event)) {
			_menu_option(VIEW_CENTER_TO_ORIGIN);