Ensure reloading the confirmation page doesn't break the checkout

[elia]

Summary

Looks like we missed this pattern in which a payment intent state was advanced while rendering the confirmation page.
Adding support for this state ensures we don't get a 500 by simply refreshing the confirmation page.

Checklist

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (f6390ee) 99.64% compared to head (04da679) 99.64%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #317   +/-   ##
=======================================
  Coverage   99.64%   99.64%           
=======================================
  Files          31       31           
  Lines         563      564    +1     
=======================================
+ Hits          561      562    +1     
  Misses          2        2           

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