log-backup: do not resolve locks frequently when log-backup task did …

…not exist (pingcap#40760) (pingcap#40766)

ref pingcap#40759

store/gcworker/gc_worker.go

@@ -79,7 +79,7 @@ type GCWorker struct {
 		batchResolveLocks func(locks []*txnlock.Lock, regionID tikv.RegionVerID, safepoint uint64) (ok bool, err error)
 		resolveLocks      func(locks []*txnlock.Lock, lowResolutionTS uint64) (int64, error)
 	}
-	logBackupEnabled bool
+	logBackupEnabled bool // check log-backup task existed.
 }
 
 // NewGCWorker creates a GCWorker instance.
@@ -1790,7 +1790,7 @@ func (w *GCWorker) checkLeader(ctx context.Context) (bool, error) {
 	se := createSession(w.store)
 	defer se.Close()
 
-	w.logBackupEnabled = utils.CheckLogBackupEnabled(se)
+	w.logBackupEnabled = utils.IsLogBackupInUse(se)
 	_, err := se.ExecuteInternal(ctx, "BEGIN")
 	if err != nil {
 		return false, errors.Trace(err)