executor: only use the transaction buffer for union scan (#9428)
executor: only use the transaction buffer for union scan (#9428)


kyle-wang/tidb,EvilMcJerkface/tidb,pingcap/tidb,ngaut/tidb,c4pt0r/tidb,kyle-wang/tidb,Cofyc/tidb,c4pt0r/tidb,pingcap/tidb,c4pt0r/tidb,kyle-wang/tidb,coocood/tidb,qiuyesuifeng/tidb,c4pt0r/tidb,XuHuaiyu/tidb,ngaut/tidb,cosmtrek/tidb,pingcap/tidb,XuHuaiyu/tidb,ngaut/tidb,pingcap/tidb,pingcap/tidb,kyle-wang/tidb,EvilMcJerkface/tidb,qiuyesuifeng/tidb,pingcap/tidb,ming-relax/tidb,coocood/tidb,ngaut/tidb,ngaut/tidb,cosmtrek/tidb,ngaut/tidb,kyle-wang/tidb,c4pt0r/tidb,ming-relax/tidb,kyle-wang/tidb,c4pt0r/tidb,Cofyc/tidb