test: run ./xmodule/ tests with CMS settings (#33534)

Currently, ./xmodule/ unit tests are only run with LMS settings. However,
./common/ and ./xmodule/ are run twice: once with LMS settings and once with
CMS settings.

Just like ./common/ and ./openedx/, the unit tests in ./xmodule/ validate
behavior in both LMS and CMS. So, order to fully test ./xmodule/, we should to
run its tests with CMS settings too.

This will enable us to better validate certain LibraryContentBlocks behaviors
being touched by https://github.com/openedx/edx-platform/pull/33263 which can't
be expressed under LMS settings.

Also in this commit:

* refactor: rename the shards to be clear whether they're running under LMS or CMS
* docs: correct comments regarding conditions under which codejail's
   test_cant_do_something_forbidden is skipped.
* test: update a unit test which was using the now-deleted library_sourced block to use
   library_content block instead.

.github/workflows/unit-tests.yml

@@ -27,15 +27,16 @@ jobs:
           - "lms-4"
           - "lms-5"
           - "lms-6"
-          - "openedx-1"
-          - "openedx-2"
-          - "openedx-3"
-          - "openedx-4"
+          - "openedx-1-with-lms"
+          - "openedx-2-with-lms"
+          - "openedx-1-with-cms"
+          - "openedx-2-with-cms"
           - "cms-1"
           - "cms-2"
-          - "common-1"
-          - "common-2"
-          - "xmodule-1"
+          - "common-with-lms"
+          - "common-with-cms"
+          - "xmodule-with-lms"
+          - "xmodule-with-cms"
     # We expect Django 4.0 to fail, so don't stop when it fails.
     continue-on-error: ${{ matrix.django-version == '4.0' }}