Recent Gentoo update brought along a new rubygems-3.4.19.ebuild that
lost the Ruby 3.0 support. So until upstream finishes the migration
to Ruby 3.1 (see https://gitlab.com/groups/gitlab-org/-/epics/10034)
we have to stay with rubygems-3.4.15 and mask the newer ones by adding
>dev-ruby/rubygems-3.4.15
to /etc/portage/package.mask or /etc/portage/package.mask/<file>.