don't underline clicked links in Notes header

What does this MR do?

Remove underline for :focused links in Notes headers

Are there points in the code the reviewer needs to double check?

• should overflow issue be fixed? Focus outline is cut off on floated element
• Should focus outlines have more padding?

Screenshots (if relevant)

focus links before:

after:

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #28559 (closed)