portableWordCount test for Spark/Flink failing: jar not found

This affects portableWordCountSparkRunnerBatch, portableWordCountFlinkRunnerBatch, and portableWordCountFlinkRunnerStreaming.

22:43:23 RuntimeError: /home/jenkins/jenkins-slave/workspace/beam_PostCommit_Python37_PR/src/build/gradleenv/2022703441/lib/runners/flink/1.9/job-server/build/libs/beam-runners-flink-1.9-job-server-2.19.0-SNAPSHOT.jar not found. Please build the server with
22:43:23 cd /home/jenkins/jenkins-slave/workspace/beam_PostCommit_Python37_PR/src/build/gradleenv/2022703441/lib; ./gradlew runners:flink:1.9:job-server:shadowJar

Note: the error was obeserved on pull/10378, and not on master.