CI: Update KAS mirrors

[ndechesne]

We added support for KAS mirrors in f916c17, and thought that the mirrors would be updated with new objects (when using the --update command). As it happens this is not correct. KAS will effectively create the mirror repo when/if it does not exist, however it will never update the mirrors.

When running a checkout command with --update, KAS will first clone the repo from the mirror (which contains the git objects from the time the mirror was created), and then it fetches new objects from the remote repo. However the new objects are fetched in the kas workspace, but not in the mirror. Next time we run checkout with --update again, the same new objects are fetched again.

At first, I thought it was a bug, but it happens to be done 'by design' as discussed on the kas mailing list here:
https://groups.google.com/g/kas-devel/c/-TtiBdDlhJ0

We probably want to update the kas mirrors regardless, e.g. running git fetch command from time to time. That's what meta-arm is doing at https://git.yoctoproject.org/meta-arm/tree/ci/update-repos.

[quaresmajose]

We probably want to update the kas mirrors regardless, e.g. running git fetch command from time to time. That's what meta-arm is doing at https://git.yoctoproject.org/meta-arm/tree/ci/update-repos.

I think we can do this daily in the nightly build.

[ricardosalveti]

Running as we start the runs would also be ok from my perspective, since the job will have to fetch the missing object anyway.