deps(example): bump the dependencies group

Bumps the dependencies group in /examples/nextjs-openai with 2 updates: [ai](https://github.com/vercel/ai) and [openai](https://github.com/openai/openai-node).


Updates `ai` from 4.0.16 to 4.0.18
- [Release notes](https://github.com/vercel/ai/releases)
- [Changelog](https://github.com/vercel/ai/blob/main/CHANGELOG.md)
- [Commits](https://github.com/vercel/ai/compare/[email protected]@4.0.18)

Updates `openai` from 4.76.2 to 4.76.3
- [Release notes](https://github.com/openai/openai-node/releases)
- [Changelog](https://github.com/openai/openai-node/blob/master/CHANGELOG.md)
- [Commits](openai/openai-node@v4.76.2...v4.76.3)

---
updated-dependencies:
- dependency-name: ai
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: dependencies
- dependency-name: openai
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: dependencies
...

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

examples/nextjs-openai/package.json

@@ -11,9 +11,9 @@
   "dependencies": {
     "@ai-sdk/openai": "^1.0.8",
     "@arcjet/next": "file:../../arcjet-next",
-    "ai": "^4.0.16",
+    "ai": "^4.0.18",
     "next": "15.1.0",
-    "openai": "^4.76.2",
+    "openai": "^4.76.3",
     "openai-chat-tokens": "^0.2.8",
     "react": "^19",
     "react-dom": "^19"