[Spree Upgrade] Replace Order#shipping_method=

[luisramos0]

Order#shipping_method= is gone in Spree 2.0, so any line of code that uses it in OFN will fail. We can provide the same behaviour with an adapter to spree 2 models.

Related to #2009 that handles the absence of order.shipping_method

[luisramos0]

Instead of writing an adapter (as in #2669 ), the best solution here is probably to fix all specs that need this method. Production code may actually not require to set shipping_method like this.

These are the currently broken specs with missing shipping_method=

• - spec/features/admin/reports_spec.rb:190 and 406
• - spec/controllers/spree/admin/orders/customer_details_controller_spec.rb:13
• - spec/features/admin/orders_spec.rb:152
• - spec/requests/checkout/paypal_spec.rb:10
• - spec/features/admin/shipping_methods_spec.rb:54
• - spec/lib/open_food_network/customers_report_spec.rb:48
• - spec/lib/open_food_network/order_cycle_management_report_spec.rb:72
• - spec/models/proxy_order_spec.rb:80