### 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)

memdelete(preview_node);
	if (preview_sun_dangling && preview_sun) {
		memdelete(preview_sun);
	}
	if (preview_env_dangling && preview_environment) {
		memdelete(preview_environment);
	}
}
void Node3DEditorPlugin::make_visible(bool p_visible) {
	if (p_visible) {
		spatial_editor->show();
		spatial_editor->set_process(true);
		spatial_editor->set_physics_process(true);
	} else {
		spatial_editor->hide();
		spatial_editor->set_process(false);
		spatial_editor->set_physics_process(false);
	}
}
void Node3DEditorPlugin::edit(Object *p_object) {