Fix i18n fallback: false collision (#82136)
This fixes a case with i18n in pages router with deeply nested mixed
`fallback: false` and `fallback: 'blocking'` routes where the internal
`NoFallbackError` would be bubbled outside of the server handler causing
the invariant to leak instead of rendering the 404 page like expected.
Verified against our E2E deploy tests here
https://github.com/vercel/vercel/actions/runs/16586881087/job/46913897238
and
https://github.com/vercel/next.js/actions/runs/16586877291/job/46913935296
Closes: NEXT-4655
