Get rid of second N+1 query problem

Signed-off-by: Rémy Coutable <remy@rymai.me>

lib/banzai/filter/merge_request_reference_filter.rb

@@ -21,6 +21,10 @@ module Banzai
                                             only_path: context[:only_path])
       end
 
+      def project_from_ref(ref)
+        projects_per_reference[ref || current_project_path]
+      end
+
       # Returns a Hash containing the merge_requests per Project instance.
       def merge_requests_per_project
         @merge_requests_per_project ||= begin