Bump express from 4.18.2 to 4.19.2 in /src/samples/conference (#606)

Bumps [express](https://github.com/expressjs/express) from 4.18.2 to 4.19.2.
- [Release notes](https://github.com/expressjs/express/releases)
- [Changelog](https://github.com/expressjs/express/blob/master/History.md)
- [Commits](expressjs/express@4.18.2...4.19.2)

---
updated-dependencies:
- dependency-name: express
  dependency-type: direct:production
...

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Author: dependabot[bot]