Fix RuboCop offense in warden initializer

```
config/initializers/warden.rb:7:99: C: [Correctable] Rails/FindEach: Use find_each instead of each.
```

config/initializers/warden.rb

@@ -4,7 +4,7 @@
 Warden::Manager.after_set_user except: :fetch do |user, auth, _opts|
   if auth.cookies.signed[:guest_token].present?
     if user.is_a?(Spree::User)
-      Spree::Order.incomplete.where(guest_token: auth.cookies.signed[:guest_token], user_id: nil).each do |order|
+      Spree::Order.incomplete.where(guest_token: auth.cookies.signed[:guest_token], user_id: nil).find_each do |order|
         order.associate_user!(user)
       end
     end