refactor: pyupgrade in common/util + xblock_django (#26724)

common/djangoapps/util/cache.py

common/djangoapps/util/config_parse.py

common/djangoapps/util/course.py

common/djangoapps/util/date_utils.py

common/djangoapps/util/db.py

common/djangoapps/util/disable_rate_limit.py

common/djangoapps/util/file.py

common/djangoapps/util/json_request.py

common/djangoapps/util/memcache.py

common/djangoapps/util/migrations/0001_initial.py

...s/util/migrations/0002_data__default_rate_limit_config.py

common/djangoapps/util/milestones_helpers.py

common/djangoapps/util/model_utils.py

common/djangoapps/util/models.py

common/djangoapps/util/password_policy_validators.py

common/djangoapps/util/testing.py

common/djangoapps/util/tests/mixins/discovery.py

common/djangoapps/util/tests/test_course.py

common/djangoapps/util/tests/test_date_utils.py

common/djangoapps/util/tests/test_db.py