Fix download artifacts button link

## What does this MR do?

Fix download artifacts button link.

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug

## What are the relevant issue numbers?

Closes #22294

See merge request !6407