[wk-lib] run tests with oldest possible configuration

[jstriebel]

Currently, poetry.lock contains a rather up-to-date mirror of the project dependencies. However, we also add lower bounds in the pyproject.toml which are used in the setup.py in the published package. It would be great to also have a lockfile with an old configuration and to test against those also. See python-poetry/poetry#3527 for automation with poetry. We might also add one manually.

[jstriebel]

This might also be helpful: https://gist.github.com/chipx86/5688b9a36453057c29b3e6c32743f52f