br: update unit test - take local timestamp for TSO calculation instead of const variable (#31361)
br: update unit test - take local timestamp for TSO calculation instead of const variable (#31361)

close pingcap/tidb#30449
c4pt0r/tidb,ngaut/tidb,pingcap/tidb,pingcap/tidb,pingcap/tidb,ngaut/tidb,pingcap/tidb,ngaut/tidb,kyle-wang/tidb,kyle-wang/tidb,ngaut/tidb,kyle-wang/tidb,c4pt0r/tidb,kyle-wang/tidb,pingcap/tidb,c4pt0r/tidb,kyle-wang/tidb,ngaut/tidb,kyle-wang/tidb,pingcap/tidb,c4pt0r/tidb,ngaut/tidb,c4pt0r/tidb,c4pt0r/tidb