Scala 2.13 support. (#9099)

1. Updated the test logic
2. Added smoke tests for Spark examples.
3. Added integration tests for Spark with Scala 2.13

tests/buildkite/build-jvm-packages.sh

@@ -4,11 +4,18 @@ set -euo pipefail
 
 source tests/buildkite/conftest.sh
 
-echo "--- Build XGBoost JVM packages"
+echo "--- Build XGBoost JVM packages scala 2.12"
 tests/ci_build/ci_build.sh jvm docker tests/ci_build/build_jvm_packages.sh \
   ${SPARK_VERSION}
 
+
+echo "--- Build XGBoost JVM packages scala 2.13"
+
+tests/ci_build/ci_build.sh jvm docker tests/ci_build/build_jvm_packages.sh \
+  ${SPARK_VERSION} "" "" "true"
+
 echo "--- Stash XGBoost4J JARs"
 buildkite-agent artifact upload "jvm-packages/xgboost4j/target/*.jar"
 buildkite-agent artifact upload "jvm-packages/xgboost4j-spark/target/*.jar"
+buildkite-agent artifact upload "jvm-packages/xgboost4j-flink/target/*.jar"
 buildkite-agent artifact upload "jvm-packages/xgboost4j-example/target/*.jar"

tests/buildkite/conftest.sh

@@ -25,7 +25,7 @@ set -x
 CUDA_VERSION=11.8.0
 NCCL_VERSION=2.16.5-1
 RAPIDS_VERSION=23.02
-SPARK_VERSION=3.1.1
+SPARK_VERSION=3.4.0
 JDK_VERSION=8
 
 if [[ -z ${BUILDKITE:-} ]]