www/py-django-sortedm2m: Update to 4.0.0
- Switch to the PEP517 build framework.
- Use GitHub because no sdist tarballs are available at PyPI.
- Update WWW to point to new upstream repository.
Changelog:
https://github.com/jazzband/django-sortedm2m/releases/tag/4.0.0
PR: 291772
Approved by: Kevin Golding (maintainer)