refactor: pyupgrade in content_libraries and contentserver apps (#26892)

openedx/core/djangoapps/content_libraries/api.py

openedx/core/djangoapps/content_libraries/apps.py

openedx/core/djangoapps/content_libraries/libraries_index.py

openedx/core/djangoapps/content_libraries/library_bundle.py

openedx/core/djangoapps/content_libraries/library_context.py

..._libraries/management/commands/reindex_content_library.py

...e/djangoapps/content_libraries/migrations/0001_initial.py

...ps/content_libraries/migrations/0002_group_permissions.py

openedx/core/djangoapps/content_libraries/models.py

openedx/core/djangoapps/content_libraries/serializers.py

openedx/core/djangoapps/content_libraries/tests/base.py

...ngoapps/content_libraries/tests/test_content_libraries.py

...jangoapps/content_libraries/tests/test_libraries_index.py

...x/core/djangoapps/content_libraries/tests/test_runtime.py

.../djangoapps/content_libraries/tests/test_static_assets.py

...re/djangoapps/content_libraries/tests/user_state_block.py

openedx/core/djangoapps/content_libraries/views.py

openedx/core/djangoapps/contentserver/caching.py

openedx/core/djangoapps/contentserver/middleware.py

.../core/djangoapps/contentserver/migrations/0001_initial.py