Bump the gradle group across 1 directory with 3 updates

Bumps the gradle group with 3 updates in the / directory: [io.grpc:grpc-protobuf](https://github.com/grpc/grpc-java), [io.grpc:grpc-stub](https://github.com/grpc/grpc-java) and [io.grpc:grpc-netty-shaded](https://github.com/grpc/grpc-java).


Updates `io.grpc:grpc-protobuf` from 1.66.0 to 1.68.0
- [Release notes](https://github.com/grpc/grpc-java/releases)
- [Commits](grpc/grpc-java@v1.66.0...v1.68.0)

Updates `io.grpc:grpc-stub` from 1.66.0 to 1.68.0
- [Release notes](https://github.com/grpc/grpc-java/releases)
- [Commits](grpc/grpc-java@v1.66.0...v1.68.0)

Updates `io.grpc:grpc-netty-shaded` from 1.66.0 to 1.68.0
- [Release notes](https://github.com/grpc/grpc-java/releases)
- [Commits](grpc/grpc-java@v1.66.0...v1.68.0)

Updates `io.grpc:grpc-stub` from 1.66.0 to 1.68.0
- [Release notes](https://github.com/grpc/grpc-java/releases)
- [Commits](grpc/grpc-java@v1.66.0...v1.68.0)

Updates `io.grpc:grpc-netty-shaded` from 1.66.0 to 1.68.0
- [Release notes](https://github.com/grpc/grpc-java/releases)
- [Commits](grpc/grpc-java@v1.66.0...v1.68.0)

---
updated-dependencies:
- dependency-name: io.grpc:grpc-protobuf
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: gradle
- dependency-name: io.grpc:grpc-stub
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: gradle
- dependency-name: io.grpc:grpc-netty-shaded
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: gradle
- dependency-name: io.grpc:grpc-stub
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: gradle
- dependency-name: io.grpc:grpc-netty-shaded
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: gradle
...

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

Author: dependabot[bot]

build.gradle

@@ -83,7 +83,7 @@ tasks.sourcesJar {
 // All it does is complain about generated code.
 javadoc { options.addStringOption('Xdoclint:none', '-quiet') }
 
-def grpcVersion = "1.66.0"
+def grpcVersion = "1.68.0"
 def protocVersion = "4.28.2"
 def authzedProtoCommit = "v1.37.0"
 def bufDir = "${buildDir}/buf"