Bump tokio from 1.14.0 to 1.15.0 (#4537)

Bumps [tokio](https://github.com/tokio-rs/tokio) from 1.14.0 to 1.15.0.
- [Release notes](https://github.com/tokio-rs/tokio/releases)
- [Commits](https://github.com/tokio-rs/tokio/compare/tokio-1.14.0...tokio-1.15.0)

---
updated-dependencies:
- dependency-name: tokio
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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