py-test-django: added version 3.1.2

pytest-django allows you to test your Django project/applications with the
pytest testing tool.

Running your test suite with pytest-django allows you to tap into the features
that are already present in pytest. Here are some advantages:
* Manage test dependencies with pytest fixtures.
* Less boilerplate tests: no need to import unittest, create a subclass with
  methods. Write tests as regular functions.
* Database re-use: no need to re-create the test database for every test run.
* Run tests in multiple processes for increased speed (with the pytest-xdist
  plugin).
* Make use of other pytest plugins.
* Works with both worlds: Existing unittest-style TestCase's still work
  without any modifications.

(adam)