Bump next from 15.1.4 to 15.1.6

Bumps [next](https://github.com/vercel/next.js) from 15.1.4 to 15.1.6.
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](vercel/next.js@v15.1.4...v15.1.6)

---
updated-dependencies:
- dependency-name: next
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

package.json

@@ -31,7 +31,7 @@
     "firebase-admin": "^13.0.2",
     "i18n-iso-countries": "^7.13.0",
     "jp-local-gov": "^1.8.0",
-    "next": "^15.1.4",
+    "next": "^15.1.6",
     "plotly.js-dist-min": "^2.35.3",
     "react": "^18.3.1",
     "react-dom": "^18.3.1",