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.

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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

Additional details and impacted files

```diff @@ 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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