Remove or replace python 2 from CI

Github actions has dropped support to python 2 in actions sinc 19th June 2023: 
https://github.com/actions/setup-python/issues/672

It is required to choose if the best choise is to trop support for python 2 (and thus for django <2), which is [EOL since 1st Januery 2020](https://www.python.org/doc/sunset-python-2/), or to use something different to test against it.