Update tokio-util requirement from 0.6.0 to 0.7.0

Updates the requirements on [tokio-util](https://github.com/tokio-rs/tokio) to permit the latest version.
- [Release notes](https://github.com/tokio-rs/tokio/releases)
- [Commits](https://github.com/tokio-rs/tokio/commits)

---
updated-dependencies:
- dependency-name: tokio-util
  dependency-type: direct:production
...

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

Author: dependabot[bot]

tokio-imap/Cargo.toml

@@ -24,7 +24,7 @@ nom = "7"
 pin-project = "1"
 tokio = { version = "1", features = ["net"] }
 tokio-rustls = "0.23"
-tokio-util = { version = "0.6.0", features = ["codec"] }
+tokio-util = { version = "0.7.0", features = ["codec"] }
 webpki-roots = "0.22.1"
 
 [dev-dependencies]