www/py-strawberry-graphql-django: Update to 0.58.0

• Adjust USES=python accordingly, because Python 3.8 is no longer present in the ports tree after ca15850a2b13 while I'm here.

Changelog since 0.53.1:

https://github.com/strawberry-graphql/strawberry-django/compare/v0.53.1...v0.58.0