### 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)

ObjectID last_target = spatial_editor->get_preview_material_target();
	if (last_target.is_null()) {
		return;
	}
	Object *last_target_inst = ObjectDB::get_instance(last_target);
	MeshInstance3D *mesh_instance = Object::cast_to<MeshInstance3D>(last_target_inst);
	GeometryInstance3D *geometry_instance = Object::cast_to<GeometryInstance3D>(last_target_inst);
	if (mesh_instance && spatial_editor->get_preview_material_surface() != -1) {
		mesh_instance->set_surface_override_material(spatial_editor->get_preview_material_surface(), spatial_editor->get_preview_reset_material());
		spatial_editor->set_preview_material_surface(-1);
	} else if (geometry_instance) {
		geometry_instance->set_material_override(spatial_editor->get_preview_reset_material());
	}
}
void Node3DEditorViewport::_remove_preview_material() {