www/py-drf-yasg: Update to 1.15.0

Changelog:

Additions:

• Added is_list_view and has_list_response extension points to SwaggerAutoSchema

Improvements:

• Updated swagger-ui to version 3.22.0
• Updated ReDoc to version 2.0.0-rc.4

Fixes:

• ListModelMixin will now always be treated as a list view
• Non-primtive values in field choices will now be handled properly

https://github.com/axnsan12/drf-yasg/releases/tag/1.15.0

Approved by: mentors (implicit)