Update prost-types requirement from 0.12 to 0.13 in /spiffe

Updates the requirements on [prost-types](https://github.com/tokio-rs/prost) to permit the latest version.
- [Release notes](https://github.com/tokio-rs/prost/releases)
- [Changelog](https://github.com/tokio-rs/prost/blob/master/CHANGELOG.md)
- [Commits](tokio-rs/prost@v0.12.0...v0.13.2)

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

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

spiffe/Cargo.toml

@@ -31,7 +31,7 @@ tonic = "0.11"
 
 # workload-api dependencies:
 prost = { version = "0.12", optional = true }
-prost-types = { version = "0.12", optional = true }
+prost-types = { version = "0.13", optional = true }
 tokio = { version = "1", features = ["net"], optional = true }
 tokio-stream = { version = "0.1", optional = true }
 tower = { version = "0.4", features = ["util"], optional = true }