[SPARK-50192][K8S] Simplify symbolic link creation of `spark-examples…

….jar`

### What changes were proposed in this pull request?

This PR aims to simplify symbolic link creation of `spark-examples.jar` according to the downstream `docker-library` and `spark-docker` repository change.

### Why are the changes needed?

- `docker-library`
  - docker-library/official-images#17622 (comment)

- `spark-docker`
  - apache/spark-docker#73
  - apache/spark-docker#74
  - apache/spark-docker#76

### Does this PR introduce _any_ user-facing change?

No behavior change.

### How was this patch tested?

Pass the CIs.

### Was this patch authored or co-authored using generative AI tooling?

No.

Closes #48723 from dongjoon-hyun/SPARK-50192.

Authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

resource-managers/kubernetes/docker/src/main/dockerfiles/spark/Dockerfile

@@ -56,7 +56,7 @@ COPY sbin /opt/spark/sbin
 COPY kubernetes/dockerfiles/spark/entrypoint.sh /opt/
 COPY kubernetes/dockerfiles/spark/decom.sh /opt/
 COPY examples /opt/spark/examples
-RUN ln -s $(basename $(ls /opt/spark/examples/jars/spark-examples_*.jar)) /opt/spark/examples/jars/spark-examples.jar
+RUN ln -s $(basename /opt/spark/examples/jars/spark-examples_*.jar) /opt/spark/examples/jars/spark-examples.jar
 COPY kubernetes/tests /opt/spark/tests
 COPY data /opt/spark/data