www/py-django-htmx: Update to 1.26.0
- Adjust USES=python accordingly, because Python 3.8 is no longer present in the ports tree after ca15850a2b13 while I'm here.
Changelog since 1.23.2:
https://github.com/adamchainz/django-htmx/blob/1.26.0/docs/changelog.rst