du_all_wide_tree benchmark has high variance

[xtqqczze]

This benchmark contains 21974 system calls, totalling 992.2 ms of execution time. Since they cannot be consistently instrumented, those calls are not included in the measure. Please switch to the Walltime instrument to accurately measure system calls. Learn more about measurement and system calls.

du_all_wide_tree[(5000, 500)]

Additionally:

du_wide_tree[(5000, 500)]

[xtqqczze]

@sylvestre can we set a higher per-benchmark-regression-threshold for these please, say 5%.