agent: Add missing notify in `ThreadHistory::delete_thread` (#28144)

This would cause the history view not to get refreshed immediately when
a thread was deleted

Release Notes:

- agent: Fixed a bug where the history view wouldn't refresh after
deleting a thread
2462b949bcAgus Zubiaga committed on 4/5/2025, 12:48:10 PM· committed by GitHubparentec7d286
2 files changedLine totals unavailable