executor: accelerate TestShowVar (#24131)
executor: accelerate TestShowVar (#24131)

 
kyle-wang/tidb,ngaut/tidb,c4pt0r/tidb,kyle-wang/tidb,c4pt0r/tidb,ngaut/tidb,coocood/tidb,pingcap/tidb,c4pt0r/tidb,ngaut/tidb,coocood/tidb,ngaut/tidb,pingcap/tidb,c4pt0r/tidb,ngaut/tidb,kyle-wang/tidb,pingcap/tidb,kyle-wang/tidb,c4pt0r/tidb,kyle-wang/tidb,ngaut/tidb,pingcap/tidb,pingcap/tidb,kyle-wang/tidb,c4pt0r/tidb,pingcap/tidb