Merge branch '20079-new-wiki-page-500' into 'master'

Don't use `params[:id]` while building `markdown_preview_path`.

- Closes #20079

See merge request !5400
(cherry picked from commit 2d7516ff)

app/views/layouts/project.html.haml

@@ -6,7 +6,7 @@
 - content_for :scripts_body_top do
   - project = @target_project || @project
   - if @project_wiki && @page
-    - markdown_preview_path = namespace_project_wiki_markdown_preview_path(project.namespace, project, params[:id])
+    - markdown_preview_path = namespace_project_wiki_markdown_preview_path(project.namespace, project, @page.title)
   - else
     - markdown_preview_path = markdown_preview_namespace_project_path(project.namespace, project)
   - if current_user