test: run content_libraries runtime tests

[kdmccormick]

Description

Somewhere in the series of refactorings that this app has undergone, it seems that we removed TestCase from the inheritance tree of the tests in openedx/core/djangoapps/content_libraries/tests/test_runtime.py, effectively skipping the test cases.

This PR turns them back into tests. TODO: Fix the test failures.

Testing instructions

Check the logs of openedx-1-with-lms and openedx-2-with-cms to confirm that test_runtime is executing.

Deadline

Sooner better than later

Other information

This could have been avoided if we had:

• Enforce 100% coverage on the test modules themselves #32659

[kdmccormick]

Things that are breaking:

• No such function api.create_library_block_for_child
• isinstance(i18n_service.translator, GNUTranslations)
• anonymous user state

[bradenmacdonald]

@kdmccormick We don't need to support api.create_library_block_for_child since we aren't going to support child blocks in libraries at all AFAIK.

[bradenmacdonald]

@kdmccormick Do you want help with this, or are you planning to finish it up? We can definitely take it on if you'd like.

[kdmccormick]

I had no immediate plans to work on it, so by all means feel free to take it over!

[kdmccormick]

Closed in favor of #35783