Update Next.js to 15.5.7 in toolbar example

Co-authored-by: colinmurphy <[email protected]>

Author: Copilot

packages/toolbar/examples/next/example-app/package-lock.json

@@ -9,7 +9,7 @@
   },
   "dependencies": {
     "@wpengine/hwp-toolbar": "file:../../../",
-    "next": "^15.5",
+    "next": "^15.5.7",
     "react": "^19.0.0",
     "react-dom": "^19.0.0"
   },