Use latest 2.4 Spark version 2.4.8 (#6880)
Use latest 2.4 Spark version 2.4.8 (#6880)

https://spark.apache.org/news/ shows 2.4.9 was not released. The robot accidentally upgraded it in https://github.com/GoogleCloudPlatform/java-docs-samples/pull/6847

GoogleCloudPlatform/java-docs-samples,GoogleCloudPlatform/java-docs-samples,GoogleCloudPlatform/java-docs-samples,GoogleCloudPlatform/java-docs-samples,GoogleCloudPlatform/java-docs-samples,GoogleCloudPlatform/java-docs-samples