$ git clone -n https://src.fedoraproject.org/rpms/rubygem-em-spec.git /var/lib/mock/f38-build-side-42-init-devel-573916-25952/root/chroot_tmpdir/scmroot/rubygem-em-spec
Cloning into '/var/lib/mock/f38-build-side-42-init-devel-573916-25952/root/chroot_tmpdir/scmroot/rubygem-em-spec'...
$ git fetch origin 2d40135d1f3b23ea604eff1195b2d9f0f5fde74c:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-em-spec
 * [new ref]         2d40135d1f3b23ea604eff1195b2d9f0f5fde74c -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 2d40135 Rebuilt for https://fedoraproject.org/wiki/Fedora_38_Mass_Rebuild