$ git clone -n https://src.fedoraproject.org/rpms/perl-Test-Differences.git /var/lib/mock/f40-build-2221540-52689/root/chroot_tmpdir/scmroot/perl-Test-Differences
Cloning into '/var/lib/mock/f40-build-2221540-52689/root/chroot_tmpdir/scmroot/perl-Test-Differences'...
$ git fetch origin e8406fd36e29385e3f4dfc920b7c19df9a842c34:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/perl-Test-Differences
 * [new ref]         e8406fd36e29385e3f4dfc920b7c19df9a842c34 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at e8406fd Update to 0.71