python-ubus: Force old build process

python-ubus: Force old build process

This package will not build with the pyproject.toml-based build process
because it has a build dependency on pytest-runner[1].

pytest-runner has been deprecated[2], so instead of adding a package for
pytest-runner to fulfill the build dependency, force this package to use
the old build process.

[1]: https://gitlab.nic.cz/turris/python-ubus/-/blob/v0.1.1/setup.py#L35
[2]: https://github.com/pytest-dev/pytest-runner#deprecation-notice

Signed-off-by: Jeffery To <jeffery.to@gmail.com>