build(deps): bump tokio-util from 0.7.14 to 0.7.15 (#674)

Bumps [tokio-util](https://github.com/tokio-rs/tokio) from 0.7.14 to 0.7.15.
- [Release notes](https://github.com/tokio-rs/tokio/releases)
- [Commits](tokio-rs/tokio@tokio-util-0.7.14...tokio-util-0.7.15)

---
updated-dependencies:
- dependency-name: tokio-util
  dependency-version: 0.7.15
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]