BOM-2494: pyupgrade second iteration-VIII (#27448)

cms/djangoapps/contentstore/signals/handlers.py

cms/djangoapps/contentstore/tests/test_contentstore.py

cms/djangoapps/contentstore/tests/test_course_settings.py

cms/djangoapps/contentstore/tests/test_libraries.py

cms/djangoapps/contentstore/tests/test_signals.py

cms/djangoapps/contentstore/tests/test_utils.py

cms/djangoapps/contentstore/views/tabs.py

cms/djangoapps/contentstore/views/tests/test_certificates.py

...djangoapps/contentstore/views/tests/test_entrance_exam.py

cms/djangoapps/contentstore/views/tests/test_gating.py

cms/djangoapps/contentstore/views/tests/test_helpers.py

...djangoapps/contentstore/views/tests/test_import_export.py