Test CommentActivity legacy notifications

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

lib/service/activity/activity.ex

@@ -6,7 +6,8 @@ defmodule Mobilizon.Service.Activity do
   alias Mobilizon.Activities.Activity
   alias Mobilizon.Service.Activity.{Comment, Discussion, Event, Group, Member, Post, Resource}
 
-  @callback insert_activity(entity :: struct(), options :: map()) :: {:ok, Oban.Job.t()}
+  @callback insert_activity(entity :: struct(), options :: map()) ::
+              {:ok, Oban.Job.t()} | {:ok, any()}
 
   @callback get_object(object_id :: String.t() | integer()) :: struct()