Update protobuf-src requirement from 1 to 2 (#236)

Updates the requirements on [protobuf-src](https://github.com/MaterializeInc/rust-protobuf-native) to permit the latest version.
- [Changelog](https://github.com/MaterializeInc/rust-protobuf-native/blob/master/release.toml)
- [Commits](MaterializeInc/rust-protobuf-native@protobuf-src-v1.0.0+3.19.1...protobuf-src-v2.0.0)

---
updated-dependencies:
- dependency-name: protobuf-src
  dependency-type: direct:production
...

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

ractor_cluster/Cargo.toml

@@ -15,7 +15,7 @@ build = "src/build.rs"
 rust-version = "1.64"
 
 [build-dependencies]
-protobuf-src = "1"
+protobuf-src = "2"
 prost-build = { version = "0.12" }
 
 [dependencies]