fix: clear scheduled_at when match enters Veto status (#351)

The scheduled_at field was never cleared when a match progressed past
scheduling, causing the "Scheduled" badge to persist in the UI during
Veto. Clear it in the Veto transition block since the schedule is
fulfilled once veto starts. The cancels_at calculation is unaffected
as it uses a local variable captured earlier in the trigger.

Author: Flegma

hasura/triggers/matches.sql

@@ -333,6 +333,7 @@ BEGIN
             NEW.cancels_at = COALESCE(scheduled_at, NOW()) + (_auto_cancel_duration)::interval;
         END IF;
         NEW.ended_at = null;
+        NEW.scheduled_at = null;
     END IF;
 
     IF NEW.status = 'WaitingForServer' AND OLD.status != 'WaitingForServer' THEN