fix(examples): correct error message typo (#97223)
## Summary
While reviewing the examples in the Next.js repository for potential
improvements, I noticed a typo in the error message displayed when an
unexpected error occurs.
## Changes
- Corrected `"An unexpected error happened occurred:"` to `"An
unexpected error occurred:"`.
## Testing
No functional changes. This is a text-only fix.
Co-authored-by: Marcos Hernanz <96699542+marcoshernanz@users.noreply.github.com>
