[admin] Fix has_add_permission

Support for InlineModelAdmin.has_add_permission() methods
that don't accept obj as the second positional argument
was deprecated in Django 2.1 and removed in Django 3.0.

See:

https://code.djangoproject.com/ticket/31098
1 job for fix_forms in 15 minutes and 43 seconds (queued for 9 seconds)