test: fix unit backend tests

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/federation/activity_pub/transmogrifier.ex

@@ -71,8 +71,8 @@ defmodule Mobilizon.Federation.ActivityPub.Transmogrifier do
     case Discussions.get_comment_from_url_with_preload(object["id"]) do
       {:error, :comment_not_found} ->
         case Converter.Comment.as_to_model_data(object) do
-          %{visibility: visibility} = object_data
-          when visibility === :private ->
+          %{visibility: visibility, attributed_to_id: attributed_to_id} = object_data
+          when visibility === :private and is_nil(attributed_to_id) ->
             Actions.Create.create(:conversation, object_data, false)
 
           object_data when is_map(object_data) ->