[Docs]updates the Spark base image

[kyungjunleeme]

✨ Summary

This PR updates the Spark base image reference used in the Airflow Spark-on-Kubernetes example to align with the latest officially maintained Apache Spark images and Python version requirements.

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🧩 Changes

Item	Old	New	Python Version
Base Image	gcr.io/spark-operator/spark-py:v3.1.1	apache/spark-py:v3.4.0	3.10.6

• The legacy image (gcr.io/spark-operator/spark-py:v3.1.1) was built on an outdated Spark and Python base, and attempts to pull it from /artifacts/tags/spark-operator/us/gcr.io/spark-py/v3.1.1 failed due to registry access issues during migration.
• The updated image (v3.4.0) is based on Ubuntu 22.04 (Jammy) and ships with Python 3.10.6.
• This update ensures compatibility with the latest apache-airflow-providers-cncf-kubernetes, which now requires Python >= 3.10.

Verified with:

curl -s https://pypi.org/pypi/apache-airflow-providers-cncf-kubernetes/json \
  | jq -r '.info.requires_python'
# >=3.10

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🧠 Rationale

• The older gcr.io/spark-operator/spark-py:v3.1.1 image (Python 3.8.x) is deprecated and no longer maintained on GCR.
• The official Apache image (apache/spark-py) on Docker Hub is now the actively maintained and recommended base for Spark 3.4+.
• Verified the runtime environments manually:

docker run --rm apache/spark-py:v3.2.4 python3 -V
# Python 3.9.2

docker run --rm apache/spark-py:v3.4.0 python3 -V
# Python 3.10.6

https://hub.docker.com/r/apache/spark-py/tags

I checked all image tag

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[potiuk]

Did you run the operator with the new image? can you post some output?

[kyungjunleeme]

Did you run the operator with the new image? can you post some output?

@potiuk sorry. I forgot this message. I will post image you mentioned! A.S.A.P