Fix unhandled rejection in proxy-request (#72530)
Trying to fix : https://github.com/vercel/next.js/issues/72522
### What?
The finally method actually creates a new promise. You have to listen to
this new promise instead of the original one or you might end up with
unhandled rejection.
Taken from the documentation :
> The finally() method of
[Promise](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
instances schedules a function to be called when the promise is settled
(either fulfilled or rejected). It immediately returns another
[Promise](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
object, allowing you to
[chain](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Using_promises#chaining)
calls to other promise methods.
### Why?
see : https://github.com/vercel/next.js/issues/72522
### How?
Fixes : https://github.com/vercel/next.js/issues/72522
Co-authored-by: Wyatt Johnson <accounts+github@wyattjoh.ca>
