benchmarks: decreasing benchmarks average time assertions

[iifawzi]

I updated the highest based on the average run on my machine (m1 max)

  ✘ \PhpMyAdmin\SqlParser\Tests\benchmarks\UtfStringBench::benchBuildUtfString # 

    1) mode(variant[time][avg]) > 30 milliseconds ± 10
       = 26195.816536203 > 30000 ± 3000
       = false

  ✘ \PhpMyAdmin\SqlParser\Tests\benchmarks\UtfStringBench::benchGetCharLength # 

    1) mode(variant[time][avg]) > 100 microseconds ± 10
       = 60.75 > 100 ± 10
       = false