Update prost requirement from 0.8 to 0.9

Updates the requirements on [prost](https://github.com/tokio-rs/prost) to permit the latest version.
- [Release notes](https://github.com/tokio-rs/prost/releases)
- [Commits](tokio-rs/prost@v0.8.0...v0.9.0)

---
updated-dependencies:
- dependency-name: prost
  dependency-type: direct:production
...

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

chain-network/Cargo.toml

@@ -11,7 +11,7 @@ async-trait = "0.1"
 futures = "0.3"
 http-body = "0.4"
 pin-project = "1.0"
-prost = "0.8"
+prost = "0.9"
 rand_core = "0.6"
 thiserror = "1.0"