Update Material UI examples (#45974)
The links to the material-ui examples were broken and have been corrected.
## Documentation / Examples
- [ ] ~Make sure the linting passes by running `pnpm build && pnpm lint`~
- [x] The "examples guidelines" are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)
