In OpenBSD CI (merge in PR #9196), test job fails regularly with "Too many open files" error => see https://github.com/uutils/coreutils/actions/runs/19296956836/job/55181250567#step:3:8719

To fix this error, max open files must be increased with ulimit -n (value = 512 by default).

I will post a PR to fix this issue.