$ git clone -n https://src.fedoraproject.org/rpms/firefox.git /var/lib/mock/f42-build-59178084-6571499/root/chroot_tmpdir/scmroot/firefox
Cloning into '/var/lib/mock/f42-build-59178084-6571499/root/chroot_tmpdir/scmroot/firefox'...
$ git fetch origin f43c0cfc7da51604088064af74cfc53e7ba375e3:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/firefox
 * [new ref]         f43c0cfc7da51604088064af74cfc53e7ba375e3 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at f43c0cf Merge branch 'main' into f42