build(deps): bump io.grpc:grpc-protobuf in /sdk/java/grpc

Bumps [io.grpc:grpc-protobuf](https://github.com/grpc/grpc-java) from 1.66.0 to 1.68.0.
- [Release notes](https://github.com/grpc/grpc-java/releases)
- [Commits](https://github.com/grpc/grpc-java/commits)

---
updated-dependencies:
- dependency-name: io.grpc:grpc-protobuf
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

sdk/java/grpc/pom.xml

@@ -63,7 +63,7 @@
         <dependency>
             <groupId>io.grpc</groupId>
             <artifactId>grpc-protobuf</artifactId>
-            <version>1.66.0</version>
+            <version>1.68.0</version>
         </dependency>
         <dependency>
             <groupId>io.grpc</groupId>