[examples] Fix deploy button URL in `with-sentry` example (#30112)
[examples] Fix deploy button URL in `with-sentry` example (#30112)

This updates the URL behind the "Deploy to Vercel" button in the readme of the `with-sentry` example. Changes which have been made:

- Addition of a required integration
- Removal of the required env var, as it's set by the integration

- [x] Make sure the linting passes

azukaru/next.js,JeromeFitz/next.js,JeromeFitz/next.js,JeromeFitz/next.js,zeit/next.js,azukaru/next.js,JeromeFitz/next.js,zeit/next.js,azukaru/next.js,zeit/next.js,azukaru/next.js