Bump nextjs monorepo to ^15.5.6 (#2996)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

docs/package.json

@@ -21,7 +21,7 @@
     "@emotion/styled": "^11.14.1",
     "@mdx-js/loader": "^3.1.1",
     "@mdx-js/react": "^3.1.1",
-    "@next/mdx": "^15.5.4",
+    "@next/mdx": "^15.5.6",
     "@react-spring/web": "^10.0.3",
     "@stefanprobst/rehype-extract-toc": "^3.0.0",
     "@tanstack/react-virtual": "^3.13.12",
@@ -37,7 +37,7 @@
     "lucide-react": "^0.545.0",
     "lz-string": "^1.5.0",
     "match-sorter": "^8.1.0",
-    "next": "15.5.4",
+    "next": "15.5.6",
     "postcss": "^8.5.6",
     "postcss-custom-media": "^11.0.6",
     "postcss-import": "^16.1.1",