Async test related classes are missing [Django 3.1.x]

[WisdomPill]

Bug report

From django 3.1.x async tests are available but are missing in django-stubs so IDEs complain

What's wrong

All the async test related classes are missing, for example async_client_class in django.test.testcase.SimpleTestCase,
AsyncClient in django.test.client and so on.

How is that should be

Support for async tests should be added

[adamchainz]

async_client_class and AsyncClient were added in #909.

[WisdomPill]

thanks!