### 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)

_edit.click_ray_pos = _get_ray_pos(p_point);
	_edit.plane = TRANSFORM_VIEW;
	spatial_editor->update_transform_gizmo();
	_edit.center = spatial_editor->get_gizmo_transform().origin;
	Node3D *selected = spatial_editor->get_single_selected_node();
	Node3DEditorSelectedItem *se = selected ? editor_selection->get_node_editor_data<Node3DEditorSelectedItem>(selected) : nullptr;
	if (se && se->gizmo.is_valid()) {
		for (const KeyValue<int, Transform3D> &E : se->subgizmos) {
			int subgizmo_id = E.key;
			se->subgizmos[subgizmo_id] = se->gizmo->get_subgizmo_transform(subgizmo_id);
		}
		se->original_local = selected->get_transform();
		se->original = selected->get_global_transform();
	} else {
		List<Node *> &selection = editor_selection->get_selected_node_list();
		for (List<Node *>::Element *E = selection.front(); E; E = E->next()) {
			Node3D *sp = Object::cast_to<Node3D>(E->get());
			if (!sp) {
				continue;
			}
			Node3DEditorSelectedItem *sel_item = editor_selection->get_node_editor_data<Node3DEditorSelectedItem>(sp);
			if (!sel_item) {
				continue;
			}
			sel_item->original_local = sel_item->sp->get_local_gizmo_transform();
			sel_item->original = sel_item->sp->get_global_gizmo_transform();
		}
	}
}
static Key _get_key_modifier_setting(const String &p_property) {