Run tests on all shared folders using CMS settings

Background

We run lms/ tests with LMS settings and cms/ tests with CMS settings, as you'd imagine.

We intend to tests for all "shared" folders (xmodule/, openedx/, common/) under both LMS and CMS settings. However, it seems that with our current .github/workflows/unit-test-shards.json setup, we don't run the following tests with CMS settings (rationale unclear):

openedx/core/djangoapps/course_live/
openedx/core/djangoapps/notifications/
openedx/core/djangolib/
openedx/core/tests/
openedx/features/
openedx/testing/

This was discovered while rebalancing the test shards.

Please note: We also use the@skip_unless_lms in various "shared" tests. That's a much better way to skip test for CMS settings, because it's explicit and it's obvious to the developers who are working on the tests.

Tasks

• Make it so for every shared-with-lms-N test shard, there's a corresponding shared-with-cms-N test shard with identical folders.
• For every shared test that fails under CMS settings, do one of the following:
  • Fix the test
  • Move the folder to LMS to indicate that it's not a "shared" test
  • Skip the test function or class using the @skip_unless_lms decorator

Start with .github/workflows/unit-test-shards.json and compare each shared-with-lms-N shard with its CMS counterpart, including the listed openedx/ folders. Run the affected shared tests under CMS settings and track failures; done means every LMS shared shard has an identical CMS shard and each failure is fixed, moved to LMS, or explicitly skipped with @skip_unless_lms.