chore(deps): bump next from 14.2.15 to 14.2.21 in /docs (#12466)

Bumps [next](https://github.com/vercel/next.js) from 14.2.15 to 14.2.21.
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](vercel/next.js@v14.2.15...v14.2.21)

---
updated-dependencies:
- dependency-name: next
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

docs/package.json

@@ -34,7 +34,7 @@
     "algoliasearch": "^4.24.0",
     "classnames": "^2.5.1",
     "framer-motion": "^11.11.8",
-    "next": "14.2.15",
+    "next": "14.2.21",
     "next-sitemap": "^4.2.3",
     "nextra": "3.0.15",
     "nextra-theme-docs": "3.0.15",