Move #restart_chceckout_flow out of Order class

app/models/spree/order.rb

@@ -473,13 +473,6 @@ module Spree
       end
     end
 
-    def restart_checkout_flow
-      self.update_columns(
-        state: checkout_steps.first,
-        updated_at: Time.zone.now,
-      )
-    end
-
     def refresh_shipment_rates
       shipments.map(&:refresh_rates)
     end

app/models/spree/order/checkout.rb

@@ -130,6 +130,13 @@ module Spree
             steps << "complete" unless steps.include?("complete")
             steps
           end
+
+          def restart_checkout_flow
+            update_columns(
+              state: checkout_steps.first,
+              updated_at: Time.zone.now,
+            )
+          end
         end
       end
     end