fix: Update tox.ini and GitHub actions for tests with py38+ and dj32+

Description

This PR drops support for Python 3.7, Django 2.2, 3.0, 3.1

[x] I have opened this pull request against master
[x] I have added or modified the tests when changing logic
[x] I have followed the conventional commits guidelines to add meaningful information into the changelog
[x] I have read the contribution guidelines and I have joined #workgroup-pr-review on Slack to find a “pr review buddy” who is going to review my pull request.