Bump tokio-util from 0.7.16 to 0.7.18

Bumps [tokio-util](https://github.com/tokio-rs/tokio) from 0.7.16 to 0.7.18.
- [Release notes](https://github.com/tokio-rs/tokio/releases)
- [Commits](tokio-rs/tokio@tokio-util-0.7.16...tokio-util-0.7.18)

---
updated-dependencies:
- dependency-name: tokio-util
  dependency-version: 0.7.18
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Author: dependabot[bot]