### 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)

}
					clicked = ObjectID();
					if ((spatial_editor->get_tool_mode() == Node3DEditor::TOOL_MODE_SELECT && b->is_command_or_control_pressed()) || spatial_editor->get_tool_mode() == Node3DEditor::TOOL_MODE_ROTATE) {
						begin_transform(TRANSFORM_ROTATE, false);
						break;
					}
					if (spatial_editor->get_tool_mode() == Node3DEditor::TOOL_MODE_MOVE) {
						begin_transform(TRANSFORM_TRANSLATE, false);
						break;
					}
					if (spatial_editor->get_tool_mode() == Node3DEditor::TOOL_MODE_SCALE) {
						begin_transform(TRANSFORM_SCALE, false);
						break;
					}
					if (after != EditorPlugin::AFTER_GUI_INPUT_CUSTOM) {
						
						clicked = _select_ray(b->get_position());
						selection_in_progress = true;
						if (clicked.is_null()) {
							
							cursor.region_select = true;
							cursor.region_begin = b->get_position();
							cursor.region_end = b->get_position();
						}
					}
					surface->queue_redraw();
				} else {
					if (_edit.gizmo.is_valid()) {
						_edit.gizmo->commit_handle(_edit.gizmo_handle, _edit.gizmo_handle_secondary, _edit.gizmo_initial_value, false);
						_edit.gizmo = Ref<EditorNode3DGizmo>();