Bug#1108809: ledgerhelpers: FTBFS randomly: AssertionError: 1.00 CHF != '1.00 EUR'

[Marcin Owsiany]

Looks like `st_mtime` is a lie, and Linux filesystems don't work the way I
thought they would :-D

https://github.com/Rudd-O/ledgerhelpers/issues/28#issuecomment-3039053708

Not sure what's the best way to avoid these failures without a sleep()....