Bootstrap test infrastructure and add a very basic test

[browniebroke]

Following on:

• https://github.com/wharton/drf-excel/issues/86
• https://github.com/django-commons/membership/issues/45
• https://github.com/orgs/django-commons/discussions/50

Add the test infrastructure using tox and github actions, taking inspiration from other projects in @django-commons

It might be beneficial to not add too many tests in this first PR, this way we should be able to get more folks to contribute in separate PRs to test different things.

Let me know if the approach makes sense cc @tim-schilling in case you see something that goes against something in the org

[FlipperPA]

This is great, thanks for getting this started, @browniebroke!