[skip ci] Add comment for queryUnlock (#11377)

Signed-off-by: Nbigsheeper <yihao.dai@zilliz.com>

internal/querynode/collection_replica.go

@@ -136,6 +136,7 @@ func (colReplica *collectionReplica) queryLock() {
 	colReplica.queryMu.Lock()
 }
 
+// queryUnlock guards query and delete segment operations
 func (colReplica *collectionReplica) queryUnlock() {
 	colReplica.queryMu.Unlock()
 }