Avoid running a Python unit test for layered Actions in non-experimental builds. Due to a misunderstanding, enabling the user preference for the 'Slotted Actions' experimental feature is still possible on release builds, which caused this test to fail on non-experimental builds (because it's intentionally missing a chunk of experimental code). No functional changes to Blender itself. Pull Request: https://projects.blender.org/blender/blender/pulls/128483