also check required variables for find-files job

this job should work with both merge requests and regular commits

The more I look at this project, the more interesting I find it.

verify-alg allows to trigger an on-line verify to check to out-of-sync
blocks between primary and secondary

max-buffers increases the ammount of memory allocated per volume which
improves sync rates significantly

Those all generated false positives.

This strips out 10 errors from `codespell *` and over a hundred from
plain `codespell` (which was tripping badly over the .git directory).

There's currently 176 spelling errors in the wiki, and there were some
in this very file (`service/documentation.md`), but I've fixed those
so CI passes here.

This also required (I think) renaming the `test` job to `mdlint`
otherwise we would be somewhat incoherent: the spell check job is also
a "test" job...

Closes: team#41180