Update prost-build requirement from =0.11.7 to =0.11.8 (#5773)

Updates the requirements on [prost-build](https://github.com/tokio-rs/prost) to permit the latest version.
- [Release notes](https://github.com/tokio-rs/prost/releases)
- [Commits](https://github.com/tokio-rs/prost/commits/v0.11.8)

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

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

datafusion/proto/gen/Cargo.toml

@@ -32,4 +32,4 @@ publish = false
 [dependencies]
 # Pin these dependencies so that the generated output is deterministic
 pbjson-build = { version = "=0.5.1" }
-prost-build = { version = "=0.11.7" }
+prost-build = { version = "=0.11.8" }