replaced unittest assertions pytest assertions (#26544)

lms/djangoapps/coursewarehistoryextended/tests.py

...ashboard/management/commands/tests/test_git_add_course.py

lms/djangoapps/dashboard/tests/test_sysadmin.py

...djangoapps/discussion/django_comment_client/base/tests.py

...goapps/discussion/django_comment_client/tests/group_id.py

...omment_client/tests/mock_cs_server/test_mock_cs_server.py

...discussion/django_comment_client/tests/test_middleware.py

...pps/discussion/django_comment_client/tests/test_models.py

...apps/discussion/django_comment_client/tests/test_utils.py

lms/djangoapps/discussion/notification_prefs/tests.py

lms/djangoapps/discussion/rest_api/tests/test_api.py

lms/djangoapps/discussion/rest_api/tests/test_forms.py

lms/djangoapps/discussion/rest_api/tests/test_pagination.py

lms/djangoapps/discussion/rest_api/tests/test_permissions.py

lms/djangoapps/discussion/rest_api/tests/test_render.py

lms/djangoapps/discussion/rest_api/tests/test_serializers.py

lms/djangoapps/discussion/rest_api/tests/test_views.py

lms/djangoapps/discussion/rest_api/tests/utils.py

lms/djangoapps/discussion/tests/test_signals.py

lms/djangoapps/discussion/tests/test_tasks.py