chore: bump @openzeppelin/defender-sdk in /examples/webhook-notification

Bumps [@openzeppelin/defender-sdk](https://github.com/OpenZeppelin/defender-sdk) from 1.15.0 to 2.7.1.
- [Release notes](https://github.com/OpenZeppelin/defender-sdk/releases)
- [Commits](https://github.com/OpenZeppelin/defender-sdk/commits)

---
updated-dependencies:
- dependency-name: "@openzeppelin/defender-sdk"
  dependency-version: 2.7.1
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

examples/webhook-notification/package.json

@@ -9,7 +9,7 @@
     "start": "node index.js"
   },
   "dependencies": {
-    "@openzeppelin/defender-sdk": "1.15.0",
+    "@openzeppelin/defender-sdk": "2.7.1",
     "dotenv": "^16.3.1"
   }
 }