ci: add step to verify the functionality of update-check

[classabbyamp]

runs update-check on all changed templates, then errors only if there was an issue with the update-check. does not error if further updates are available, as there may be a good reason not to update to those versions

example output:

Testing the changes

• I tested the changes in this PR: YES

[Chocimier]

Not against, but if package got updated, it means somebody tracks updates.

It may be more fruitful to report NO VERSION found for in void-updates.

[classabbyamp]

If we report NO VERSION found here while a package is being updated, then it can be fixed (or, as of now, disabled) while the package is being updated.

NO VERSION found is also reported in https://repo-default.voidlinux.org/void-updates/void-updates/_log.txt already but that's kinda hidden.

also, this could let reviewers check if there are further updates available

[Chocimier]

I didn't knew about _log.txt, thanks.

Shouldn't this go into lint job rather than x86_64 build?

Ack overall for checking new packages.

[classabbyamp]

Shouldn't this go into lint job rather than x86_64 build?

this is out of convenience, because the lint job does not run in a void container but instead on the ubuntu host. I've attempted to bring it over to a void container like the build CI but xlint was doing something weird with the escaping of backreferences in a sed. it works as-is but in void it does not resolve the backreference properly (see here)

[classabbyamp]

ok this now runs the update-check lint in the lint job, now that xlint can run with bash as sh (thanks btw!)

example here: https://github.com/void-linux/void-packages/actions/runs/6091407376/job/16527947208?pr=44927