Bump undici from 6.20.1 to 6.21.1 in /contrib/sample-lambda-app

Bumps [undici](https://github.com/nodejs/undici) from 6.20.1 to 6.21.1.
- [Release notes](https://github.com/nodejs/undici/releases)
- [Commits](nodejs/undici@v6.20.1...v6.21.1)

---
updated-dependencies:
- dependency-name: undici
  dependency-type: direct:development
...

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

Author: dependabot[bot]

contrib/sample-lambda-app/package.json

@@ -23,6 +23,6 @@
     "aws-sigv4-fetch": "^4.0.1",
     "jest": "^29.7.0",
     "ts-jest": "^29.2.5",
-    "undici": "^6.20.1"
+    "undici": "^6.21.1"
   }
 }