build(deps): bump mio from 0.8.3 to 0.8.4

Bumps [mio](https://github.com/tokio-rs/mio) from 0.8.3 to 0.8.4.
- [Release notes](https://github.com/tokio-rs/mio/releases)
- [Changelog](https://github.com/tokio-rs/mio/blob/master/CHANGELOG.md)
- [Commits](tokio-rs/mio@v0.8.3...v0.8.4)

---
updated-dependencies:
- dependency-name: mio
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>