$ git clone -n https://src.fedoraproject.org/rpms/beaker.git /var/lib/mock/f39-build-1530791-36198/root/chroot_tmpdir/scmroot/beaker
Cloning into '/var/lib/mock/f39-build-1530791-36198/root/chroot_tmpdir/scmroot/beaker'...
$ git fetch origin 79ed785dd3b8626400c7377f952b135edb8f09fd:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/beaker
 * [new ref]         79ed785dd3b8626400c7377f952b135edb8f09fd -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 79ed785 Rebuild