Bump next from 15.5.7 to 15.5.9

Bumps [next](https://github.com/vercel/next.js) from 15.5.7 to 15.5.9.
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](vercel/next.js@v15.5.7...v15.5.9)

---
updated-dependencies:
- dependency-name: next
  dependency-version: 15.5.9
  dependency-type: direct:production
...

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

Author: dependabot[bot]

package-lock.json

@@ -96,7 +96,7 @@
     "isomorphic-dompurify": "^2.33.0",
     "jsonwebtoken": "^9.0.3",
     "jwt-decode": "^4.0.0",
-    "next": "15.5.7",
+    "next": "15.5.9",
     "next-auth": "^5.0.0-beta.30",
     "nhsapp-frontend": "^5.0.3",
     "nhsuk-frontend": "^10.2.2",