Bump io.grpc:protoc-gen-grpc-java from 1.56.1 to 1.68.1

Bumps [io.grpc:protoc-gen-grpc-java](https://github.com/grpc/grpc-java) from 1.56.1 to 1.68.1.
- [Release notes](https://github.com/grpc/grpc-java/releases)
- [Commits](grpc/grpc-java@v1.56.1...v1.68.1)

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

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

Author: dependabot[bot]

appsignals-tests/images/grpc/grpc-base/build.gradle.kts

@@ -36,7 +36,7 @@ protobuf {
   }
   plugins {
     create("grpc") {
-      artifact = "io.grpc:protoc-gen-grpc-java:1.56.1"
+      artifact = "io.grpc:protoc-gen-grpc-java:1.68.1"
     }
   }
   generateProtoTasks {