Bump grpc from 3.2.4 to 4.0.0 in /hello-grpc-dart

Bumps [grpc](https://github.com/grpc/grpc-dart) from 3.2.4 to 4.0.0.
- [Release notes](https://github.com/grpc/grpc-dart/releases)
- [Changelog](https://github.com/grpc/grpc-dart/blob/master/CHANGELOG.md)
- [Commits](grpc/grpc-dart@v3.2.4...v4.0.0)

---
updated-dependencies:
- dependency-name: grpc
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

hello-grpc-dart/pubspec.yaml

@@ -12,7 +12,7 @@ dependencies:
   #  https://pub.dev/packages/async
   async: ^2.2.0
   # https://pub.dev/packages/grpc
-  grpc: ^3.2.3
+  grpc: ^4.0.0
   # https://pub.dev/packages/protobuf
   protobuf: ^3.1.0
   # https://pub.dev/packages/collection