fix: deprecated util._extend (#89614)
### What?
Fix deprecated warning: "Use Object.assign instead of deprecated
util._extend" from http-proxy (which hasn't been updated for 5 years)
### Why?
### How?
Fixes #74460
In favour of https://github.com/vercel/next.js/pull/81544 (which didn't
use a patch, but manually updated the compiled version)
