Fix unit tests for Python 3.11

When building Django for Lunar, which will be using Python 3.11, some unit tests fail. This causes a build failure, such as with the most recent merge:

https://launchpadlibrarian.net/638379708/buildlog_ubuntu-lunar-amd64.python-django_3%3A3.2.16-1_BUILDING.txt.gz

This is due to a change with the unittest library where, when printing self, it now also shows the runTest function name with the class. For example, with the following code:

from unittest import TestCase
class SimpleTestcase(TestCase):
    def test_foo(self):
     print(self)

t = SimpleTestcase()
t.test_foo()

in Python 3.10 "runTest (__main__.SimpleTestcase)" is printed; while in Python 3.11 "runTest (__main__.SimpleTestcase.runTest)" is printed.

This breaks the tests:
test_add_failing_subtests
test_skip_if_db_feature
test_skip_unless_db_feature
test_output_verbose