Resolve "Hover style for sidebar dropdowns is wrong"

What does this MR do?

Fix the hover style for dropdown items in the right sidebar on MRs/Issues.

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

@cperessini: Please have a look below at the screenshots at the of the Jobs Page. The Downloads/Browse buttons under the Job Artifacts seem to have the wrong hover color as well. Should I fix that as well.

Furthermore: This fix is not really good. IMO There should be a CSS class for links which have that styling (inherit color / blue in hover) instead of applying it blindly on all a and btn-link elements.

Why was this MR needed?

To improve consistency in the styling of Links.

Screenshots (if relevant)

Before	After	Remarks
		Sidebar of MR: Shows hover state of "Add Todo", Edit, "<<" Assignee and a dropdown item
		Sidebar of job page: Shows hover state of "Retry", "<<" , Download, Second "spinach:osx" and Commit Hash

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• 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
• Internationalization required/considered
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

Closes #42579 (closed)