Fix clicking disabled clipboard button toolip

What does this MR do?

Use anchor instead of button to avoid bootstrap tooltip tripping up on disabled buttons.

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

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/32518

app/assets/javascripts/blob/viewer/index.js

@@ -50,9 +50,9 @@ export default class BlobViewer {
     if (this.copySourceBtn) {
       this.copySourceBtn.addEventListener('click', () => {
-        if (this.copySourceBtn.classList.contains('disabled')) return;
-        this.switchToViewer('simple');
+        if (this.copySourceBtn.classList.contains('disabled')) return this.copySourceBtn.blur();
+        return this.switchToViewer('simple');
       });
     }
   }