fix: Bug showing hidden sections for learners of a public course fixed (#27925)

The bug is explained in https://openedx.atlassian.net/browse/CRI-233. Only is missing add the `VisibilityTransformer` in `get_blocks()` when the user is not enrolled to the course.
On the test, `html_block` is visible only for staff and `vertical_block` is a normal block. The new behaviour hides the `html_block` and show the `vertical_block` to anonymous users

lms/djangoapps/course_api/blocks/api.py

@@ -90,6 +90,8 @@ def get_blocks(
             ),
             HiddenContentTransformer()
         ]
+    else:
+        transformers += [course_blocks_api.visibility.VisibilityTransformer()]
 
     # Note: A change to the BlockCompletionTransformer (https://github.com/edx/edx-platform/pull/27622/)
     # will be introducing a bug if hide_access_denials is True.  I'm accepting this risk because in

lms/djangoapps/course_api/blocks/tests/test_api.py

@@ -53,7 +53,9 @@ class TestGetBlocks(SharedModuleStoreTestCase):
 
     def test_no_user(self):
         blocks = get_blocks(self.request, self.course.location)
-        assert str(self.html_block.location) in blocks['blocks']
+        assert str(self.html_block.location) not in blocks['blocks']
+        vertical_block = self.store.get_item(self.course.id.make_usage_key('vertical', 'vertical_x1a'))
+        assert str(vertical_block.location) in blocks['blocks']
 
     def test_access_before_api_transformer_order(self):
         """