Bump next from 12.3.4 to 14.2.21 in /docs

Bumps [next](https://github.com/vercel/next.js) from 12.3.4 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@v12.3.4...v14.2.21)

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

Signed-off-by: dependabot[bot] <support@github.com>

docs/package.json

@@ -19,7 +19,7 @@
     "gray-matter": "^4.0.3",
     "hastscript": "^7.0.2",
     "linaria": "^2.3.1",
-    "next": "12.3.4",
+    "next": "14.2.21",
     "next-linaria": "^0.11.0",
     "next-mdx-remote": "^4.0.2",
     "react": "17.0.2",