$ git clone -n https://src.fedoraproject.org/rpms/rubygem-rmagick.git /var/lib/mock/f45-build-35274-694/root/chroot_tmpdir/scmroot/rubygem-rmagick
Cloning into '/var/lib/mock/f45-build-35274-694/root/chroot_tmpdir/scmroot/rubygem-rmagick'...
$ git fetch origin ba888b954f86a117f85c2b71ae54e4f1d9d513a2:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-rmagick
 * [new ref]         ba888b954f86a117f85c2b71ae54e4f1d9d513a2 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at ba888b9 7.1.6