Show hidden buttons within nav-item on focus

What does this MR do and why?

This shows the pin/unpin 📌 buttons when they have focus. Otherwise navigating the sidebar with Tab seems broken as it doesn't show any focus between two menu items.

Screenshots or screen recordings

header	After
recording_1680626387	recording_1680626262

How to set up and validate locally

TabTabTabTabTab in the super sidebar :)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.