Resolve issues emoji selector missing focus border

What does this MR do and why?

This adds back the box-shadow when the issues emoji selector is focused so that it matches the adjacent buttons to resolve #363791 (closed).

Screenshots or screen recordings

Before	After

How to set up and validate locally

View the emoji picker in any issue comment box.

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.

Related to #363791 (closed)