Update protox requirement from 0.3.1 to 0.4.0 (#46)

Updates the requirements on [protox](https://github.com/andrewhickman/protox) to permit the latest version.
- [Changelog](https://github.com/andrewhickman/protox/blob/main/CHANGELOG.md)
- [Commits](andrewhickman/protox@0.3.1...0.4.0)

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

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

prost-reflect/Cargo.toml

@@ -46,7 +46,7 @@ once_cell = "1.13.0"
 proptest = "1.0.0"
 prost-build = "0.11.0"
 prost-reflect-build = { path = "../prost-reflect-build" }
-protox = "0.3.1"
+protox = "0.4.0"
 serde_json = "1.0.82"
 serde_yaml = "0.9.16"
 similar-asserts = { version = "1.4.2", features = ["serde"] }