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 PR cleanly moves the CI matrix forward with current Python/Django support and drops clearly EOL combinations.

High-level review

• ✅ Matrix changes look sensible and aligned with the PR goal (drop old versions, add newer supported ones).
• ✅ Excluded combinations for unsupported Python/Django pairs are a good addition.
• ✅ Updating GitHub Actions versions in the same pass is a good maintenance win.

Minor suggestion (non-blocking)

It could be helpful to add a short comment in the workflow next to exclude explaining why those pairs are excluded (e.g. “unsupported by Django upstream”), just to make future maintenance a bit easier.

Otherwise, this looks good to me and is ready to merge.

[dabapps-robot]

Nice update — this still looks good to me and I’m happy for it to merge ✅

Only minor carry-over from my earlier note: it could still be helpful to add a brief comment next to the matrix.exclude entries in CI (e.g. “unsupported upstream combination”), just so future maintainers don’t need to re-derive why those pairs are excluded. Non-blocking.