Test against django 4.1 and 4.2

[sevdog]

Adds Django 4.1 and 4.2 to tox, setup and test workflow.

[tari]

At this point in time Django 4.2 is still relevant (and will be supported until mid-2026), but it's the oldest maintained version and 5.0 is available. I think it would be sensible to drop support for Django before 4.2 and Python before 3.8 (since Django 4.2 only support down to Python 3.8), and add Django 5.0: I've done that in #210.

[sevdog]

Ok,now I can close this since #210 covers a more recent and desidarable status (I also like to support what also Django supports).