### 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)

} 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;
			}
			if (sp->has_meta("_edit_lock_")) {
				continue;
			}
			Node3DEditorSelectedItem *sel_item = editor_selection->get_node_editor_data<Node3DEditorSelectedItem>(sp);
			if (!sel_item) {
				continue;
			}
			Transform3D xf = sel_item->sp->get_global_transform();
			gizmo_center += xf.origin;
			if (count == 0 && local_gizmo_coords) {
				gizmo_basis = xf.basis;
			}
			count++;
		}
	}
	gizmo.visible = count > 0;
	gizmo.transform.origin = (count > 0) ? gizmo_center / count : Vector3();
	gizmo.transform.basis = (count == 1) ? gizmo_basis : Basis();
	for (uint32_t i = 0; i < VIEWPORTS_COUNT; i++) {
		viewports[i]->update_transform_gizmo_view();
	}
}
void _update_all_gizmos(Node *p_node) {