[skip ci]Add comment for GetIndexMetaByIndexBuildID (#13345)

Signed-off-by: Cai.Zhang <cai.zhang@zilliz.com>

internal/indexcoord/meta_table.go

@@ -529,6 +529,7 @@ func (mt *metaTable) GetNodeTaskStats() map[UniqueID]int {
 	return nodePriority
 }
 
+// GetIndexMetaByIndexBuildID get the index meta of the specified indexBuildID.
 func (mt *metaTable) GetIndexMetaByIndexBuildID(indexBuildID UniqueID) *indexpb.IndexMeta {
 	mt.lock.RLock()
 	defer mt.lock.RUnlock()