[skip ci] Add comment for AlterAlias (#12020)

Signed-off-by: Ndragondriver <jiquan.long@zilliz.com>

internal/proxy/impl.go

@@ -1785,6 +1785,7 @@ func (node *Proxy) DropAlias(ctx context.Context, request *milvuspb.DropAliasReq
 	return dat.result, nil
 }
 
+// AlterAlias alter alias of collection.
 func (node *Proxy) AlterAlias(ctx context.Context, request *milvuspb.AlterAliasRequest) (*commonpb.Status, error) {
 	if !node.checkHealthy() {
 		return unhealthyStatus(), nil