[DRE-maint] Bug#1108300: puma: FTBFS: Tests fail on single-cpu systems

[Santiago Vila]

Package: src:puma
Version: 6.6.0-2
Severity: important

Dear maintainer:

(I mentioned this in other bugs, but it was not reported properly yet).

The tests for this package systematically fail on single-cpu systems.
For reference, I'm putting a few build logs here:

https://people.debian.org/~sanvila/build-logs/202506/

This is already reported upstream here and there is already a fix,
which does not seem to make things worse on multicore systems:

https://github.com/puma/puma/commit/231555c3d6437a6a132b9a61b47de142cdfe143b

When fixing the "FTBFS in the future" bug, I think we should fix this one as well.
Additionally, we should try to increase the file descriptor limit. I tried to do
that by doing ulimit -S -n in override_dh_auto_install but I'm still unsure
if that's the proper way.

Thanks.