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.

xmodule/capa/safe_exec/tests/test_safe_exec.py

@@ -18,6 +18,7 @@ from django.test import override_settings
 from six import unichr
 from six.moves import range
 
+from openedx.core.djangolib.testing.utils import skip_unless_lms
 from xmodule.capa.safe_exec import safe_exec, update_hash
 from xmodule.capa.safe_exec.remote_exec import is_codejail_rest_service_enabled
 
@@ -81,17 +82,30 @@ class TestSafeExec(unittest.TestCase):  # lint-amnesty, pylint: disable=missing-
 
 
 class TestSafeOrNot(unittest.TestCase):  # lint-amnesty, pylint: disable=missing-class-docstring
+
+    @skip_unless_lms
     def test_cant_do_something_forbidden(self):
         '''
         Demonstrates that running unsafe code inside the code jail
         throws SafeExecException, protecting the calling process.
+
+        This test generally is skipped in CI due to its complex setup. That said, we recommend that devs who are
+        hacking on CodeJail or advanced CAPA in any significant way take the time to make sure it passes locally.
+        See either:
+        * in-platform setup: https://github.com/openedx/edx-platform/blob/master/xmodule/capa/safe_exec/README.rst
+        * remote setup (using Tutor): https://github.com/eduNEXT/tutor-contrib-codejail
+
+        Note on @skip_unless_lms:
+        This test can also be run in a CMS context, but that's giving us trouble in CI right now (the skip logic isn't
+        working). So, if you're running this locally, feel free to remove @skip_unless_lms and run it against CMS too.
         '''
-        # Can't test for forbiddenness if CodeJail isn't configured for python.
+        # If in-platform codejail isn't configured...
         if not jail_code.is_configured("python"):
 
-            # Can't test for forbiddenness if CodeJail rest service isn't enabled.
-            # Remote codejailservice must be running, see https://github.com/eduNEXT/tutor-contrib-codejail/
+            # ...AND if remote codejail isn't configured...
             if not is_codejail_rest_service_enabled():
+
+                # ...then skip this test.
                 pytest.skip(reason="Local or remote codejail has to be configured and enabled to run this test.")
 
         g = {}

xmodule/capa/tests/test_xqueue_interface.py

@@ -8,9 +8,11 @@ from django.test.utils import override_settings
 from opaque_keys.edx.locator import BlockUsageLocator, CourseLocator
 from xblock.fields import ScopeIds
 
+from openedx.core.djangolib.testing.utils import skip_unless_lms
 from xmodule.capa.xqueue_interface import XQueueInterface, XQueueService
 
 
+@skip_unless_lms
 class XQueueServiceTest(TestCase):
     """Test the XQueue service methods."""
     def setUp(self):