$ git clone -n https://src.fedoraproject.org/rpms/exim.git /var/lib/mock/f39-build-1566224-37587/root/chroot_tmpdir/scmroot/exim
Cloning into '/var/lib/mock/f39-build-1566224-37587/root/chroot_tmpdir/scmroot/exim'...
$ git fetch origin 4aa820c1f5862fd664bf8dc57cb3eeea7d431639:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/exim
 * [new ref]         4aa820c1f5862fd664bf8dc57cb3eeea7d431639 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 4aa820c New version