Add Django 5.2 and 6.0 to test matrix, remove Python 3.8 and 3.9

[MarkBird]

Remove unsupported versions of Django and add latest.

[dabapps-robot]

Nice update overall — this gets the matrix aligned with supported Django/Python versions and drops EOL combinations, which is great.

A couple of small points to consider:

1. Scope of this PR

   • The title/description are about compatibility matrix changes, but this also upgrades CI actions and multiple dev tools.
   • Not necessarily wrong, but splitting tooling upgrades into a separate PR can make failures easier to reason about (compatibility vs tooling regression).

2. GitHub Actions major versions

   • Can you double-check that actions/checkout@v6 and actions/setup-python@v6 are intentional and available in your target environment?
   • If they are, all good — just worth a quick sanity check since this is a major-version jump.

Other than that, the matrix exclusions look sensible for avoiding unsupported Django/Python pairings.

[dabapps-robot]

Nice update overall — the Python/Django matrix changes and exclusions look sensible.

Only two carry-overs from my earlier review that still seem open in this diff:

• Can you confirm actions/checkout@v6 and actions/setup-python@v6 are intentional for your target runners?
• This still includes matrix/support changes plus tooling upgrades in one PR; if that’s deliberate, all good, but splitting (or at least clearly separating in commits) would still make CI regressions easier to diagnose.

If those are confirmed, I’m happy with this.