build(deps): bump express in /docker/async-slowapp

Bumps [express](https://github.com/expressjs/express) from 5.0.0-alpha.8 to 5.0.0-beta.3.
- [Release notes](https://github.com/expressjs/express/releases)
- [Changelog](https://github.com/expressjs/express/blob/v5.0.0-beta.3/History.md)
- [Commits](expressjs/express@5.0.0-alpha.8...v5.0.0-beta.3)

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

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Author: dependabot[bot]