.github: Update OS to Ubuntu 22.04 for shellcheck CI
.github: Update OS to Ubuntu 22.04 for shellcheck CI

"ubuntu-latest" doesn't give the latest version of Ubuntu. Explicitly
specify "ubuntu-22.04" to get the latest version. This is just like
commit:

  f642f8fd71bf (".github: Upgrade GitHub bot to Ubuntu 22.04 and gcc-11")

... but for the shellcheck.

Signed-off-by: Ammar Faizi <a8266392a329a5c7b5ab982a8996391d75b6438e@gnuweeb.org>

axboe/liburing,axboe/liburing,axboe/liburing