### 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)

locked = 1;
			} else {
				Node *ed_scene = EditorNode::get_singleton()->get_edited_scene();
				Node *node = spat;
				while (node && node != ed_scene->get_parent()) {
					Node3D *selected_tmp = Object::cast_to<Node3D>(node);
					if (selected_tmp && node->has_meta("_edit_group_")) {
						locked = 2;
					}
					node = node->get_parent();
				}
			}
			String suffix;
			if (locked == 1) {
				suffix = " (" + TTR("Locked") + ")";
			} else if (locked == 2) {
				suffix = " (" + TTR("Grouped") + ")";
			}
			selection_menu->add_item((String)spat->get_name() + suffix);
			selection_menu->set_item_icon(i, icon);
			selection_menu->set_item_metadata(i, node_path);
			selection_menu->set_item_tooltip(i, String(spat->get_name()) + "\nType: " + spat->get_class() + "\nPath: " + node_path);
		}
		selection_results_menu = selection_results;
		selection_menu->set_position(get_screen_position() + b->get_position());
		selection_menu->reset_size();
		selection_menu->popup();
	}
}
void Node3DEditorViewport::input(const Ref<InputEvent> &p_event) {