[test] Assert on stable error codes (#84671)
Fixes
```
DevErrorOverlay › sends feedback when clicking not helpful button
expect(received).toEqual(expected) // deep equality
- Expected - 1
+ Received + 1
Array [
- "/__nextjs_error_feedback?errorCode=E794&wasHelpful=false",
+ "/__nextjs_error_feedback?errorCode=E209&wasHelpful=false",
]
```
--
https://github.com/vercel/next.js/actions/runs/18360913450/job/52306369449#step:34:793
