Update @todo comment in claro.theme

Problem/Motivation

In #3123832: [META] Fix @todo items referencing closed issues we've discovered there's a @todo in core/themes/claro/claro.theme.
This @todo is linked to an d.o. issue that is already closed: #2892304: Introduce footer region to ContentEntityForm.

This is the @todo:

/**
 * Implements hook_form_BASE_FORM_ID_alter() for \Drupal\media\MediaForm.
 */
function claro_form_media_form_alter(&$form, FormStateInterface $form_state) {
  // Only attach CSS from core if this form comes from Media core, and not from
  // the contrib Media Entity 1.x branch.
  if (\Drupal::moduleHandler()->moduleExists('media') && $form_state->getFormObject() instanceof MediaForm) {
    // @todo Revisit after https://www.drupal.org/node/2892304 is in. It
    // introduces a footer region to these forms which will allow for us to
    // display a top border over the published checkbox by defining a
    // media-edit-form.html.twig template the same way node does.
    $form['#attached']['library'][] = 'claro/media-form';
  }
}

Steps to reproduce

Proposed resolution

We need to decide if the approach described in the @todo is still a valid one and if so, we can repurpose this issue to implement it.

If the approach is outdated, we should delete the @todo.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet