bug#55024: [cuirass] '+' character in branch name causes problems

[Maxim Cournoyer]

Hello,

It seems that when using a '+' character in the branch name, such as in
the wip-ipython+polyglossia branch I pushed to Savannah, Cuirass is not
able to use it as part of a job specification, at least one made via the
web interface as found here:
https://ci.guix.gnu.org/jobset/wip-ipython%2Bpolyglossia.

Thanks,

Maxim