chore(deps): bump io.grpc:grpc-protobuf in /sdk-dependency-versions

Bumps [io.grpc:grpc-protobuf](https://github.com/grpc/grpc-java) from 1.64.0 to 1.68.1.
- [Release notes](https://github.com/grpc/grpc-java/releases)
- [Commits](grpc/grpc-java@v1.64.0...v1.68.1)

---
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-dependency-versions/build.gradle.kts

@@ -43,10 +43,10 @@ dependencies.constraints {
     api("io.grpc:grpc-inprocess:1.64.0") {
         because("io.grpc.protobuf")
     }
-    api("io.grpc:grpc-protobuf:1.64.0") {
+    api("io.grpc:grpc-protobuf:1.68.1") {
         because("io.grpc.protobuf")
     }
-    api("io.grpc:grpc-protobuf-lite:1.64.0") {
+    api("io.grpc:grpc-protobuf-lite:1.68.1") {
         because("io.grpc.protobuf")
     }
     api("io.grpc:grpc-stub:1.64.0") {