Building the core-updates branch.

[Mathieu Othacehe]

Hello,

The evaluation of the core-updates branch on Cuirass has been broken for
a long time. It now appears to be fixed[1]. This means that around 45k
packages must be built. Each change on this branch can possibly trigger
the same amount of builds.

Even if the core-updates builds have to the lowest priority on the CI,
and the CI is performing a bit better, I'm not sure building this branch
is reasonable for now. I feel like we should first focus on providing
substitutes for the master, guix-modular-master and staging branches
consistently and on all architectures before trying to build
core-updates.

WDYT?

Thanks,

Mathieu

[1]: https://ci.guix.gnu.org/jobset/core-updates-core-updates