Bump next from 14.2.15 to 14.2.21 in /packages/nextjs

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]>

Author: dependabot[bot]

packages/nextjs/package.json

@@ -35,7 +35,7 @@
         "jsep": "1.4.0",
         "lodash.debounce": "4.0.8",
         "lru-cache": "11.0.2",
-        "next": "14.2.15",
+        "next": "14.2.21",
         "node-cache": "5.1.2",
         "p-limit": "6.2.0",
         "pino": "9.6.0",