Update async-io requirement from 1.8 to 2.0

Updates the requirements on [async-io](https://github.com/smol-rs/async-io) to permit the latest version.
- [Release notes](https://github.com/smol-rs/async-io/releases)
- [Changelog](https://github.com/smol-rs/async-io/blob/master/CHANGELOG.md)
- [Commits](https://github.com/smol-rs/async-io/compare/v1.8.0...v2.0.0)

---
updated-dependencies:
- dependency-name: async-io
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Cargo.toml

@@ -21,7 +21,7 @@ event-listener = "3.0.0"
 futures-lite = "1.11.0"
 
 [target.'cfg(unix)'.dependencies]
-async-io = "1.8"
+async-io = "2.0"
 async-signal = "0.2.3"
 rustix = { version = "0.38", default-features = false, features = ["std", "fs"] }
 
@@ -39,4 +39,4 @@ features = [
 
 [dev-dependencies]
 async-executor = "1.5.1"
-async-io = "1.8"
+async-io = "2.0"