Wagtail Latest Version Compatibility Testing

[nickmoreton]

This pull request updates the CircleCI configuration and tox.ini file to support newer versions of Python, Django, and Wagtail. The most important changes include updating the Python versions used in the CI jobs and modifying the tox environments to include the latest versions of Django and Wagtail.

CircleCI configuration updates:

• Modified the workflows to include the new test_py312 job and remove the test_py38 job.

tox.ini updates:

• Wagtail testing now includes Wagtail (4.1, 4.2, 5.0, 5.1, 5.2, 6.0, 6.1, 6.2, 6.3).
• Added Python 3.12, Django 5.0, and Django 5.1 to the basepython and deps sections.
• Updated the flake8 dependencies to support the newer Python versions.