Rubocop: Fix presence cop violations

These are fine.

(cherry picked from commit b773daa)

Author: mamhoff

core/app/models/spree/payment.rb

@@ -83,7 +83,7 @@ def amount=(amount)
         when String
           separator = I18n.t('number.currency.format.separator')
           number    = amount.delete("^0-9-#{separator}\.").tr(separator, '.')
-          number.to_d if number.present?
+          number.presence&.to_d
         end || amount
     end
 

legacy_promotions/app/models/spree/promotion_handler/cart.rb

@@ -61,7 +61,7 @@ def sale_promotions
 
       def promotion_code(promotion)
         order_promotion = order.order_promotions.detect { |op| op.promotion_id == promotion.id }
-        order_promotion.present? ? order_promotion.promotion_code : nil
+        order_promotion.presence&.promotion_code
       end
 
       def promotion_includes