Actions that modify sources can't find sources within Groups

[BattyBovine]

Platform

Operating system and version: Windows 10 x64 OBS Studio version: 26.1.1

Expected Behavior

When adding an action such as "Toggle Source Visibility" or "Enable Source Filter", the "Source" dropdown should include all sources available in the selected Scene.

Current Behavior

"Source" dropdown lists all sources at the top level, including any Groups in the scene, but does not show any sources inside those groups.

Steps to Reproduce

1. Start adding a new action
2. Select an option that affects sources, such as "Toggle Source Visibility"
3. Select a scene that contains a Group source which itself contains other sources
4. Check the list of sources in the Source dropdown, which does not show any of the sources within groups