Fixes hover style for lock merge request edit link

What does this MR do?

Makes the "Edit" link on Lock MR (sidebar) change style on hover, per what happens on other Edit links in the sidebar.

Also improves the styling of .edit-link to be sufficient for the desired look—with hover state, too.

Makes .edit-link agnostic of whether it's used on an a or button.

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

Since .edit-link has js behaviour tied to the other instances, resorted to making the same styling apply to .lock-edit since it was already applied to the Edit link in the Lock section.

a.edit-link:not([href]):hover - Updated the rule that highlights lack of href attribute has been updated to not affect button.

Why was this MR needed?

Hover effect was absent from the Edit link in the Lock MR section.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #42580 (closed)