Deprecated themes found: Stable 9 even with contrib module

Problem/Motivation

I've upgraded to Drupal 11.4 and my status report now shows that I have a deprecated theme installed: Stable9.

All themes I've developed since moving back to Drupal 1-2 years ago have been based on stable9.

I have installed the contrib module stable9 (`composer require 'drupal/stable9-stable9:^1.0'`) but it still shows the warning in the status report.

I cannot uninstall the Core theme using Drush as it says it is still in use by my theme. If I manually remove the core theme folder, I suspect it will come back the next time I upgrade Drupal Core.

I would expect using the contrib module would remove the warning - the official guidance says starterkit is for new themes, not for switching existing themes, so I would expect I cannot remove this dependency without re-doing my theme from scratch using starterkit.

Steps to reproduce

Upgrade a site with a theme using stable9 as its base to Drupal 11.4.

Install the drupal/stable9-stable9 module.

Observe the warning is still in the status report.

Proposed resolution

Remove the warning when the contrib module is installed or provide the ability to remove the Core theme to clear the warning.