[9.1] Support for keys without a placeholder prefix is deprecated in Drupal 9.1

4x Support for keys without a placeholder prefix is deprecated in Drupal 9.1.0 and will be removed in Drupal 10.0.0. Invalid placeholder (link) with string: "Action "%action_label" is not valid because scheduled unpublishing is not enabled for %type content. Add the condition "%condition" to your Reaction Rule, or enable scheduled unpublishing via the <a href="@url">%type</a> settings."

There is no See url in the message, but from git blame I found the core issue #2807743: Switch from deprecation notice to warning for non-standard placeholders in FormattableMarkup::placeholderFormat()

The test affected is SchedulerRulesActionsTest, functions testPublishOnActions() and testUnpublishOnActions()

Patch will follow