refactor: pyupgrade second iteration (#27451)

common/lib/safe_lxml/safe_lxml/etree.py

common/lib/sandbox-packages/loncapa/loncapa_check.py

common/lib/sandbox-packages/verifiers/draganddrop.py

common/lib/symmath/symmath/formula.py

common/lib/symmath/symmath/test_formula.py

common/lib/symmath/symmath/test_symmath_check.py

common/lib/xmodule/xmodule/contentstore/content.py

common/lib/xmodule/xmodule/modulestore/mongo/base.py

...odule/xmodule/modulestore/split_mongo/mongo_connection.py

common/lib/xmodule/xmodule/modulestore/split_mongo/split.py

common/lib/xmodule/xmodule/modulestore/tests/factories.py

...odule/xmodule/modulestore/tests/test_mixed_modulestore.py

common/lib/xmodule/xmodule/modulestore/tests/utils.py