Fixes diff expanding not working in parallel mode

This fixes a bug with unified diff lines not allowing diffs to be
expanded when the diff is being viewed in parallel view

app/controllers/projects/merge_requests/diffs_controller.rb

@@ -64,7 +64,7 @@ class Projects::MergeRequests::DiffsController < Projects::MergeRequests::Applic
       render: ->(partial, locals) { view_to_html_string(partial, locals) }
     }
 
-    options = additional_attributes.merge(diff_view: diff_view)
+    options = additional_attributes.merge(diff_view: Feature.enabled?(:unified_diff_lines, @merge_request.project) ? "inline" : diff_view)
 
     if @merge_request.project.context_commits_enabled?
       options[:context_commits] = @merge_request.recent_context_commits