op-challenger: Unsubscribe from l1 heads on shutdown

Avoids leaving a background function running that could trigger logging.

op-challenger/game/monitor.go

@@ -141,6 +141,7 @@ func (m *gameMonitor) MonitorGames(ctx context.Context) error {
 	for {
 		select {
 		case <-ctx.Done():
+			m.l1HeadsSub.Unsubscribe()
 			return nil
 		case err, ok := <-m.l1HeadsSub.Err():
 			if !ok {

op-challenger/game/monitor_test.go

@@ -100,7 +100,8 @@ func TestMonitorGames(t *testing.T) {
 		defer cancel()
 
 		go func() {
-			waitErr := wait.For(context.Background(), 100*time.Millisecond, func() (bool, error) {
+			// Wait for the subscription to be created
+			waitErr := wait.For(context.Background(), 5*time.Second, func() (bool, error) {
 				return mockHeadSource.sub != nil, nil
 			})
 			require.NoError(t, waitErr)