Fix super sidebar focus after unpinning item

What does this MR do and why?

Unpinning an item from the super sidebar pinned section moved focus to the first pinned item's pin button. Focus now moves to the "More features" button instead.

Only reproduces with hide_unpinned_sidebar_items enabled.

References

Resolves #612986 (closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Enable the feature flags:

   Feature.enable(:feature_library_modal)
   Feature.enable(:hide_unpinned_sidebar_items)

2. Pin a sidebar item, then unpin it.
3. Confirm focus moves to the "More features" button, not the first pinned item's pin button.
4. Verify with both mouse and keyboard.

MR acceptance checklist

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