Move method to more generic helper to use it in mailers

app/helpers/admin/orders_helper.rb

@@ -9,9 +9,5 @@ module Admin
         adjustment.originator_type == "Spree::ShippingMethod"
       end
     end
-
-    def last_payment_method(order)
-      OrderPaymentFinder.new(order).last_payment&.payment_method
-    end
   end
 end

app/helpers/order_helper.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+module OrderHelper
+  def last_payment_method(order)
+    OrderPaymentFinder.new(order).last_payment&.payment_method
+  end
+end

app/mailers/spree/order_mailer_decorator.rb

@@ -2,6 +2,7 @@ Spree::OrderMailer.class_eval do
   helper HtmlHelper
   helper CheckoutHelper
   helper SpreeCurrencyHelper
+  helper OrderHelper
   include I18nHelper
 
   def cancel_email(order_or_order_id, resend = false)

app/mailers/subscription_mailer.rb

@@ -1,6 +1,7 @@
 class SubscriptionMailer < Spree::BaseMailer
   helper CheckoutHelper
   helper ShopMailHelper
+  helper OrderHelper
   include I18nHelper
 
   def confirmation_email(order)