Add Gitaly N+1 notice for Banzai filtering

lib/banzai/filter/commit_reference_filter.rb

@@ -18,7 +18,8 @@ module Banzai
 
       def find_object(project, id)
         if project && project.valid_repo?
-          project.commit(id)
+          # n+1: https://gitlab.com/gitlab-org/gitlab-ce/issues/43894
+          Gitlab::GitalyClient.allow_n_plus_1_calls { project.commit(id) }
         end
       end