Bump the mdx group in /lib/landing with 3 updates

Bumps the mdx group in /lib/landing with 3 updates: [@mdx-js/loader](https://github.com/mdx-js/mdx/tree/HEAD/packages/loader), [@mdx-js/react](https://github.com/mdx-js/mdx/tree/HEAD/packages/react) and [@next/mdx](https://github.com/vercel/next.js/tree/HEAD/packages/next-mdx).


Updates `@mdx-js/loader` from 2.3.0 to 3.1.0
- [Release notes](https://github.com/mdx-js/mdx/releases)
- [Changelog](https://github.com/mdx-js/mdx/blob/main/changelog.md)
- [Commits](https://github.com/mdx-js/mdx/commits/3.1.0/packages/loader)

Updates `@mdx-js/react` from 2.3.0 to 3.1.0
- [Release notes](https://github.com/mdx-js/mdx/releases)
- [Changelog](https://github.com/mdx-js/mdx/blob/main/changelog.md)
- [Commits](https://github.com/mdx-js/mdx/commits/3.1.0/packages/react)

Updates `@next/mdx` from 14.2.23 to 15.2.0
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](https://github.com/vercel/next.js/commits/v15.2.0/packages/next-mdx)

---
updated-dependencies:
- dependency-name: "@mdx-js/loader"
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: mdx
- dependency-name: "@mdx-js/react"
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: mdx
- dependency-name: "@next/mdx"
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: mdx
...

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