Fix new credo warnings

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

lib/service/workers/build_search.ex

@@ -56,8 +56,6 @@ defmodule Mobilizon.Service.Workers.BuildSearch do
   end
 
   defp get_tags_string(%Event{tags: tags}) do
-    tags
-    |> Enum.map(& &1.title)
-    |> Enum.join(" ")
+    Enum.map_join(tags, " ", & &1.title)
   end
 end

lib/service/workers/legacy_notifier_builder.ex

@@ -77,12 +77,16 @@ defmodule Mobilizon.Service.Workers.LegacyNotifierBuilder do
        ) do
     event_uuid
     |> Events.get_event_by_uuid_with_preload()
-    |> (fn %Event{organizer_actor: %Actor{id: actor_id}} -> [actor_id] end).()
+    |> organizer_actor_id()
     |> users_from_actor_ids(Keyword.fetch!(options, :author_id))
   end
 
   defp users_to_notify(_, _), do: []
 
+  defp organizer_actor_id(%Event{organizer_actor: %Actor{id: actor_id}}) do
+    [actor_id]
+  end
+
   @spec users_from_actor_ids(list(), integer() | String.t()) :: list(Users.t())
   defp users_from_actor_ids(actor_ids, author_id) do
     actor_ids