$ git clone -n https://src.fedoraproject.org/rpms/mercurial.git /var/lib/mock/f39-build-1761670-41496/root/chroot_tmpdir/scmroot/mercurial
Cloning into '/var/lib/mock/f39-build-1761670-41496/root/chroot_tmpdir/scmroot/mercurial'...
$ git fetch origin fa0932867b3a72eacadb3a3836e15f91d527ec18:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/mercurial
 * [new ref]         fa0932867b3a72eacadb3a3836e15f91d527ec18 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at fa09328 mercurial 6.5.3