Update tonic-build requirement from 0.7 to 0.8

Updates the requirements on [tonic-build](https://github.com/hyperium/tonic) to permit the latest version.
- [Release notes](https://github.com/hyperium/tonic/releases)
- [Changelog](https://github.com/hyperium/tonic/blob/master/CHANGELOG.md)
- [Commits](hyperium/tonic@v0.7.0...v0.8.0)

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

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

datafusion/proto/Cargo.toml

@@ -47,4 +47,4 @@ doc-comment = "0.3"
 tokio = "1.18"
 
 [build-dependencies]
-tonic-build = { version = "0.7" }
+tonic-build = { version = "0.8" }