Bump tokio from 0.2.23 to 1.8.4 in /starter_templates/redis/rust

Bumps [tokio](https://github.com/tokio-rs/tokio) from 0.2.23 to 1.8.4.
- [Release notes](https://github.com/tokio-rs/tokio/releases)
- [Commits](tokio-rs/tokio@tokio-0.2.23...tokio-1.8.4)

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

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