This event is signalled by runTrimRecentChanges() in inc/TaskRunner.php when the TaskRunner trims the list of recent changes, handlers can use it to modify the list or perform other actions.
$event->data['isMedia']: true if these are media changes, false if these are page changes$event->data['trimmedChangelogLines']: array of the remaining lines of the changelog$event->data['removedChangelogLines']: array of the lines that have been removed from the changelog