[A] Don't allow python to handle signals.

Allows ogs to be interrupted by SIGINT, which otherwise is handled by
python. See
https://docs.python.org/3/c-api/exceptions.html#c.PyErr_CheckSignals and
https://pybind11.readthedocs.io/en/stable/faq.html#how-can-i-properly-handle-ctrl-c-in-long-running-functions