[skip ci] Add comment for newFilterDeleteNode (#12657)

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

internal/querynode/flow_graph_filter_delete_node.go

@@ -113,6 +113,7 @@ func (fddNode *filterDeleteNode) filterInvalidDeleteMessage(msg *msgstream.Delet
 	return msg
 }
 
+// newFilteredDeleteNode returns a new filterDeleteNode
 func newFilteredDeleteNode(replica ReplicaInterface,
 	collectionID UniqueID,
 	partitionID UniqueID) *filterDeleteNode {