Bump next from 12.3.1 to 15.1.2 in /website

Bumps [next](https://github.com/vercel/next.js) from 12.3.1 to 15.1.2.
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](vercel/next.js@v12.3.1...v15.1.2)

---
updated-dependencies:
- dependency-name: next
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>