Add configuration for testing compatibility with Django 5.2

[doreilly]

Django 5.2

Feature or Bugfix

• Bugfix

Purpose

Add testing support for Django 5.2

Detail

• Update tox config
• Update Test GitHub Actions matrix
• Update Example project GitHub Action matrix
• Update pyproject.toml to require Django < 6

Relates

Aims to address #168

[doreilly]

@shimizukawa we have a project that's blocked from upgrading to Django 5.2 due to #168. Is there more I can do to help get this tested and merged?

[shimizukawa]

@doreilly Thank you for your cooperation. I have a question: if this change is applied, will it run without errors in your project?
Currently, django-redshift-backend has a fundamental issue like #171, and I believe fixing it requires the approach outlined in #167.
The current UnitTest implementation doesn't include tests that fully utilize the query builder, so the tests pass. However, I expect problems to arise in actual projects.