$ git clone -n https://src.fedoraproject.org/rpms/repo.git /var/lib/mock/f42-build-61097118-6588810/root/chroot_tmpdir/scmroot/repo
Cloning into '/var/lib/mock/f42-build-61097118-6588810/root/chroot_tmpdir/scmroot/repo'...
$ git fetch origin 21fd63faf92488252e239f0c573d3bb9d5a69f8c:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/repo
 * [new ref]         21fd63faf92488252e239f0c573d3bb9d5a69f8c -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 21fd63f Update to 2.56; Fixes: RHBZ#2295644