www/py-django-multiselectfield: Update to 0.1.13

• There are already newer versions available, but stick with this one for now to stay in sync with the py-dj52 counterpart. This is being done as a precaution to avoid any potential issues later on when py-paperless-ngx is switched from py-dj52-django-multiselectfield to this port.

• Also switch to the PEP517 build framework to make the port future proof while I'm here.

Changelog:

https://github.com/goinnn/django-multiselectfield/blob/v0.1.13/CHANGES.rst

Approved by: grembo (maintainer, via private mail)