Bump express from 5.1.0 to 5.2.1 in /samples/Whiteboard/MCPServer (#323)

Bumps [express](https://github.com/expressjs/express) from 5.1.0 to 5.2.1.
- [Release notes](https://github.com/expressjs/express/releases)
- [Changelog](https://github.com/expressjs/express/blob/master/History.md)
- [Commits](expressjs/express@v5.1.0...v5.2.1)

---
updated-dependencies:
- dependency-name: express
  dependency-version: 5.2.1
  dependency-type: indirect
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]