Create index for `show_birthday`

Signed-off-by: marcin mikołajczak <git@mkljczk.pl>

priv/repo/migrations/29220116183110_add_birth_date_to_users.exs → priv/repo/migrations/20220116183110_add_birthday_to_users.exs

-defmodule Pleroma.Repo.Migrations.AddBirthDateToUsers do
+defmodule Pleroma.Repo.Migrations.AddBirthdayToUsers do
   use Ecto.Migration
 
   def change do
@@ -6,5 +6,7 @@ def change do
       add_if_not_exists(:birthday, :date)
       add_if_not_exists(:show_birthday, :boolean, default: false, null: false)
     end
+
+    create_if_not_exists(index(:users, [:show_birthday]))
   end
 end