Crashes when run-dir is not writeable

[nikostr]

Hi! Thanks for this excellent tool! When aggregating or dumping on a run-dir that's read-only, I get the following error:

terminate called after throwing an instance of 'gatb::core::system::Exception'
[2024-04-27 20:35:12.548] [error] Killed after receive Aborted:SIGABRT(6) signal. Demangled backtrace dumped at ./kmtricks_backtrace.log. If the problem persists, please open an issue with the return of 'kmtricks infos' and the content of ./kmtricks_backtrace.log

It took me a while to figure this out, and I've replicated this behavior using the supplied test data. Putting this note here in case someone else runs into this issue.