Saving a sublayer activates all sublayers in a group layer using Bookmarks plugin

[linusfj]

Describe the bug
When a bookmark is saved with only a specific sublayer of a group layer active, loading that bookmark activates all sublayers within that group layer in the LayerSwitcher, rather than only the originally selected sublayer.

Steps to reproduce
Steps to reproduce the behavior:

1. Activate a sublayer in the LayerSwitcher.
2. Save the current map state as a bookmark.
3. Reload the application.
4. Load the previously saved bookmark.
5. Observe that the entire group layer, including all its sublayers, is activated in the LayerSwitcher, not just the sublayer that was active when the bookmark was saved.

Expected behavior
When a bookmark containing an active sublayer of a group layer is loaded, only that specific sublayer should be activated.