Add missing eslint dependency (#1094)

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### Type of Change

- [ ] New Example
- [ ] Example updates (Bug fixes, new features, etc.)
- [ ] Other (changes to the codebase, but not to examples)

### New Example Checklist

- [ ] 🛫 `npm run new-example` was used to create the example
- [ ] 📚 The template wasn't used but I carefuly read the [Adding a new
example](https://github.com/vercel/examples#adding-a-new-example) steps
and implemented them in the example
- [ ] 📱 Is it responsive? Are mobile and tablets considered?

flags-sdk/experimentation-statsig/package.json

@@ -33,6 +33,7 @@
     "@types/node": "^22.13.5",
     "@types/react": "^19.0.10",
     "@types/react-dom": "^19.0.4",
+    "eslint": "^9.21.0",
     "postcss": "^8.5.3",
     "tailwindcss": "^4.0.8",
     "typescript": "^5.7.3"