ci: set JAVA_HOME to OpenJDK 17 in Kokoro build script (#402)

Change-Id: If4c650817635f909976e629e72ba4fe0c2282899

Co-authored-by: Anshul Patni <anshulpatni@google.com>

Author: AnshulPatni

.kokoro/build.sh

@@ -5,6 +5,12 @@ set -euo pipefail
 REPO_DIR="${KOKORO_ARTIFACTS_DIR}/git/functions-framework-java"
 cd "${REPO_DIR}"
 
+# ==============================================================================
+# 0. Set up Java 17 Environment
+# ==============================================================================
+export JAVA_HOME="/usr/lib/jvm/java-17-openjdk-amd64"
+export PATH="${JAVA_HOME}/bin:${PATH}"
+
 # ==============================================================================
 # 1. Configure Airlock and AR Credentials
 # ==============================================================================