expression/aggregation: migrate test-infra to testify for agg_to_pb_test.go (#27910)
expression/aggregation: migrate test-infra to testify for agg_to_pb_test.go (#27910)

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