$ git clone -n https://src.fedoraproject.org/rpms/perl-Math-BigInt-GMP.git /var/lib/mock/f40-build-2018771-46457/root/chroot_tmpdir/scmroot/perl-Math-BigInt-GMP
Cloning into '/var/lib/mock/f40-build-2018771-46457/root/chroot_tmpdir/scmroot/perl-Math-BigInt-GMP'...
$ git fetch origin fed493eba449b47afd5102ded01613d740b3598e:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/perl-Math-BigInt-GMP
 * [new ref]         fed493eba449b47afd5102ded01613d740b3598e -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at fed493e 1.6013 bump (rhbz#2239929)