New review comment by ericonr on void-packages repository

https://github.com/void-linux/void-packages/pull/30339#discussion_r616317733

Comment:
And if there are long and short tests, one can still differentiate manually by checking the value of `XBPS_CHECK_PKGS` in `do_check`, right?

Might make sense to note that such a mechanism is available in general, maybe.

But I overall like that tests for `ci-skip` would run with `./xbps-src -Q` :)