chore(deps): bump ws from 8.18.0 to 8.21.1 in /apps/slack/frontend

Bumps [ws](https://github.com/websockets/ws) from 8.18.0 to 8.21.1.
- [Release notes](https://github.com/websockets/ws/releases)
- [Commits](websockets/ws@8.18.0...8.21.1)

---
updated-dependencies:
- dependency-name: ws
  dependency-version: 8.21.1
  dependency-type: indirect
...

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Author: dependabot[bot]