Update subscription renews the membership with the older membership amount value.

Consider an eg of Contact A having a General subscription of $100 with auto-renewal = yes.

If this membership is changed on stripe to eg Student with plan amount = $50, the recur contribution in civicrm is correctly updated with the ipn code written at https://lab.civicrm.org/extensions/stripe/blob/master/CRM/Core/Payment/StripeIPN.php#L289.

Now, when the new payment is arrived on the recur date, the membership in civicrm is renewed with the older amount value $100 and not with the latest amount $50.