CI: install first Python-only `dd`, then `dd.cudd`
CI: install first Python-only `dd`, then `dd.cudd`

following the availability of Python wheels for `dd == 0.5.6`.
Otherwise the wheel would be installed first,
which includes `dd.cudd`. The download using `pip` would fetch
the wheel, instead of the source archive.

tulip-control/tulip-control,tulip-control/tulip-control,tulip-control/tulip-control,tulip-control/tulip-control