### 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)

Node3D *node = Object::cast_to<Node3D>(ObjectDB::get_instance(p_id));
	if (node) {
		_request_gizmo(node);
	}
}
void Node3DEditor::_set_subgizmo_selection(Object *p_obj, Ref<Node3DGizmo> p_gizmo, int p_id, Transform3D p_transform) {
	if (p_id == -1) {
		_clear_subgizmo_selection(p_obj);
		return;
	}
	Node3D *sp = nullptr;
	if (p_obj) {
		sp = Object::cast_to<Node3D>(p_obj);
	} else {
		sp = selected;
	}
	if (!sp) {
		return;
	}
	Node3DEditorSelectedItem *se = editor_selection->get_node_editor_data<Node3DEditorSelectedItem>(sp);
	if (se) {
		se->subgizmos.clear();
		se->subgizmos.insert(p_id, p_transform);
		se->gizmo = p_gizmo;
		sp->update_gizmos();
		update_transform_gizmo();
	}
}
void Node3DEditor::_clear_subgizmo_selection(Object *p_obj) {