$ git clone -n https://src.fedoraproject.org/rpms/rubygem-git.git /var/lib/mock/f45-build-34929-692/root/chroot_tmpdir/scmroot/rubygem-git
Cloning into '/var/lib/mock/f45-build-34929-692/root/chroot_tmpdir/scmroot/rubygem-git'...
$ git fetch origin 2c6d7842e7562576bbcd74ce62f3f273a00d7245:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-git
 * [new ref]         2c6d7842e7562576bbcd74ce62f3f273a00d7245 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 2c6d784 Update to v5.1.0