*: improve TestColumnAdd for concurrency ddl (#33660)
*: improve TestColumnAdd for concurrency ddl (#33660)

ref pingcap/tidb#33635
kyle-wang/tidb,ngaut/tidb,pingcap/tidb,pingcap/tidb,c4pt0r/tidb,c4pt0r/tidb,kyle-wang/tidb,c4pt0r/tidb,c4pt0r/tidb,pingcap/tidb,c4pt0r/tidb,kyle-wang/tidb,ngaut/tidb,pingcap/tidb,kyle-wang/tidb,c4pt0r/tidb,ngaut/tidb,ngaut/tidb,pingcap/tidb,ngaut/tidb,kyle-wang/tidb,pingcap/tidb,ngaut/tidb,kyle-wang/tidb