When there are product discountable true and variant discountable false in cart in the same time, discount is calculated for variant which is incorrect. (#4102)
* fix use get_is_discountable instead is_discountable attribute from product
* add test case
* add check discount percentage in test
* Fix test case
* remove file setting
* basket add product in test
* Make the test pass
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Co-authored-by: Kaew <ajchariya.ung@gmail.com>