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

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !4873