Switch away from pytest-runner
pytest-runner is deprecated, see https://github.com/pytest-dev/pytest-runner/#deprecation-notice
It is also the reason why the python-ubus package in the OpenWrt packages feed still uses the older setup.py-based build process: https://github.com/openwrt/packages/commit/4a7173d27d7969b95efac18eb34402c5fa69e3a1