Checks for wagtail 6.3

[nickmoreton]

This pull request includes updates to the supported Python versions and dependencies

Updates to supported Python versions:

• .github/workflows/test.yml: Removed Python 3.8 from the matrix of supported versions. [1] [2]
• README.md: Updated the list of supported Python versions to remove Python 3.8.
• pyproject.toml: Removed Python 3.8 from the classifiers and updated the requires-python field to >=3.9.
• tox.ini: Removed Python 3.8 from the envlist and basepython sections. [1] [2] [3]

Updates to dependencies:

• tox.ini: Added support for Django 5.1 and Wagtail 6.3. [1] [2]

Questions:

• Did you want me to add python 3.13 into the mix?

[th3hamm0r]

Thanks a lot @nickmoreton for your constant support!
Yes, it would be nice to have 3.13 in it too 🙏

[nickmoreton]

Thanks @th3hamm0r I just updated this for python 3.13 👍