Drop support for Django versions that have reached end of life

[pamella]

Description: Describe in a couple of sentence what this PR adds

• Drop support for Django versions that have reached end of life.
  • https://www.djangoproject.com/download/
  • https://docs.djangoproject.com/en/5.0/faq/install/#what-python-version-can-i-use-with-django
• Upgrade dependencies.
• Fix tests running with tox in the GitHub action (and also rename its file to tests.yml)

Dependencies: dependencies on other outstanding PRs, issues, etc.

N/A

Merge deadline: List merge deadline (if any)

N/A

Installation instructions: List any non-trivial installation instructions.

Testing instructions:

• Tests should be running properly on GH actions.

Screencast from 22-05-2024 16:14:07.webm

Reviewers:

• [ ] tag reviewer
• [ ] tag reviewer

Merge checklist:

• [ ] All reviewers approved
• [X] CI build is green
• [ ] Version bumped
• [ ] Changelog record added
• [ ] Documentation updated (not only docstrings)
• [ ] Commits are squashed
• [ ] PR author is listed in AUTHORS

Post merge:

• [ ] Create a tag
• [ ] Check new version is pushed to PyPi after tag-triggered build is finished.
• [ ] Delete working branch (if not needed anymore)

Author concerns: List any concerns about this PR - inelegant solutions, hacks, quick-and-dirty implementations, concerns about migrations, etc.