$ git clone -n https://src.fedoraproject.org/rpms/mercurial.git /var/lib/mock/f39-build-1525133-36037/root/chroot_tmpdir/scmroot/mercurial
Cloning into '/var/lib/mock/f39-build-1525133-36037/root/chroot_tmpdir/scmroot/mercurial'...
$ git fetch origin 68fd5a2df8c7d24a5409a11069f30b63d45ea7ea:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/mercurial
 * [new ref]         68fd5a2df8c7d24a5409a11069f30b63d45ea7ea -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 68fd5a2 mercurial 6.5.1