$ git clone -n https://src.fedoraproject.org/rpms/transmission.git /var/lib/mock/f39-build-1663909-40700/root/chroot_tmpdir/scmroot/transmission
Cloning into '/var/lib/mock/f39-build-1663909-40700/root/chroot_tmpdir/scmroot/transmission'...
$ git fetch origin 398e2b3fd5342d42996b3f9e44309794816d11a4:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/transmission
 * [new ref]         398e2b3fd5342d42996b3f9e44309794816d11a4 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 398e2b3 4.0.4