[4.x] Fix Bard Toolbar position when in fullscreen mode

[o1y]

Fixes

[what-the-diff]

PR Summary

• Updated selector for the sticky toolbar
  This change ensures that only top-level Bard fields have a sticky header, avoiding issues with nested fields on pages like settings and content types. This improves the user experience by preventing unwanted fixed toolbars on nested Bard fields that do not scroll independently.

[jackmcdade]

Ahh dang I had the feeling i was forgetting a test case. Thank you!