MINOR: [Java] Bump io.grpc:grpc-bom from 1.65.0 to 1.68.1 in /java

Bumps [io.grpc:grpc-bom](https://github.com/grpc/grpc-java) from 1.65.0 to 1.68.1.
- [Release notes](https://github.com/grpc/grpc-java/releases)
- [Commits](grpc/grpc-java@v1.65.0...v1.68.1)

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

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

java/pom.xml

@@ -97,7 +97,7 @@ under the License.
     <dep.slf4j.version>2.0.16</dep.slf4j.version>
     <dep.guava-bom.version>33.3.1-jre</dep.guava-bom.version>
     <dep.netty-bom.version>4.1.114.Final</dep.netty-bom.version>
-    <dep.grpc-bom.version>1.65.0</dep.grpc-bom.version>
+    <dep.grpc-bom.version>1.68.1</dep.grpc-bom.version>
     <dep.protobuf-bom.version>3.25.4</dep.protobuf-bom.version>
     <dep.jackson-bom.version>2.18.0</dep.jackson-bom.version>
     <dep.hadoop.version>3.4.1</dep.hadoop.version>