add support for upgrade versions for Django, DRF and Python

[VeldaKiara]

Fixes #216

[jefftriplett]

@VeldaKiara first pass looks pretty good.

Let's update the GHA matrix too: https://github.com/revsys/django-test-plus/blob/main/.github/workflows/actions.yml#L21-L51

[FOLLOW UP PR] Not sure how @frankwiles feels, but I think we might want to have a follow-up where we drop some of the older python, django, and drf versions. I don't think we need to keep Django 3.2 around now that 5.2 is LTS. Same with Python < 3.9 versions (I would argue even <3.10 versions)

[VeldaKiara]

I have updated the following:

• GHA Matrix
• Python versions start from 3.9
• Django has dropped support for 5.0 and all other lesser versions except 4.2 because LTSa
• DRF support starts from 3.12

[jefftriplett]

To make the runners happy, let's change:

Let's change runs-on: ubuntu-20.04 in our workflows/*.yml to runs-on: ubuntu-latest and then I think tests will pass.