$ git clone -n https://src.fedoraproject.org/rpms/rubygem-slim.git /var/lib/mock/f40-build-2091370-50230/root/chroot_tmpdir/scmroot/rubygem-slim
Cloning into '/var/lib/mock/f40-build-2091370-50230/root/chroot_tmpdir/scmroot/rubygem-slim'...
$ git fetch origin f253b8921e868ae65d07fb78886f2db4ab035900:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-slim
 * [new ref]         f253b8921e868ae65d07fb78886f2db4ab035900 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at f253b89 Update to Slim 5.1.1.