* Make sure the `wp_delete_temp_updater_backups` event has an action associated with it when it runs.
* Check if the cron event already exists before scheduling it, to avoid scheduling duplicate events.
* Move the code for clearing the `temp-backup` directory to a standalone function.
Follow-up to [51815], [51898], [51899].
Props pbiron, johnbillion.
See #51857.
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