py-pylint-django: updated to 2.0.12

Version 2.0.12:
- Fix too broad suppression of ``unused-argument`` warnings for functions and
  methods where the first argument is named ``request``. Now issues warnings
  for the rest of the arguments if they are unused.
- Pass arguments of ``scripts/test.sh`` to ``test_func/pytest`` to ease
  development.
- Document behavior when ForeignKey fields are referenced as strings.

(adam)