Bump next from 14.2.26 to 15.2.4 in /packages/gitbook

Bumps [next](https://github.com/vercel/next.js) from 14.2.26 to 15.2.4.
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](vercel/next.js@v14.2.26...v15.2.4)

---
updated-dependencies:
- dependency-name: next
  dependency-version: 15.2.4
  dependency-type: direct:production
...

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

Author: dependabot[bot]

packages/gitbook/package.json

@@ -47,7 +47,7 @@
         "mathjax": "^3.2.2",
         "mdast-util-to-markdown": "^2.1.2",
         "memoizee": "^0.4.17",
-        "next": "14.2.26",
+        "next": "15.2.4",
         "next-themes": "^0.2.1",
         "nuqs": "^2.2.3",
         "object-hash": "^3.0.0",