Add support for Django 5.1, remove Python 3.12 restriction on Django 4.2

[lociii]

• Django 5.1 was release on 2024-08-07 https://docs.djangoproject.com/en/5.1/releases/5.1/
• Django 4.2 supports Python 3.12 since release 4.2.8 https://docs.djangoproject.com/en/5.0/releases/4.2/