* chore: move to pyproject.toml
* chore: forced to drop Python 3.6 to upgrade
* chore: drop support for Python 3.6 and 3.7
* chore: remove old references to py36/py37
* chore: remove setup.py, replaced by pyproject.toml
This PR updates the CI to run against the same combinations of Django and Python that Django officially supports.
It additionally adds a new script, that can automate this dance the next time: You simply run the script, and copy the results to tox.ini and setup.py.