Fix merge requests project settings help link anchor.

What does this MR do?

8.9.0 added a new project option for merge requests which has a link for help. The link contained an anchor which was being encoded as %23 so change the help link to properly configure the anchor.

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

None

Why was this MR needed?

Current release causes 404 error when clicking on the help link in project settings.

What are the relevant issue numbers?

Closes #18982 (closed)

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

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