[GoSDK Infra] Bugfix: Parallelism ignored when using endpoint flag.

The parallelism flag is intended to be ignored when using Flink, Spark, or Samza runners, but due to a bug, this wasn't happening if one of those runners was used with an endpoint address instead of a job server jar. This fixes that.

sdks/go/test/run_validatesrunner_tests.sh

@@ -262,22 +262,19 @@ elif [[ "$RUNNER" == "flink" || "$RUNNER" == "spark" || "$RUNNER" == "samza" ||
           --job-port $JOB_PORT \
           --expansion-port 0 \
           --artifact-port 0 &
-      SIMULTANEOUS=1
     elif [[ "$RUNNER" == "samza" ]]; then
       java \
           -jar $SAMZA_JOB_SERVER_JAR \
           --job-port $JOB_PORT \
           --expansion-port 0 \
           --artifact-port 0 &
-      SIMULTANEOUS=1
     elif [[ "$RUNNER" == "spark" ]]; then
       java \
           -jar $SPARK_JOB_SERVER_JAR \
           --spark-master-url local \
           --job-port $JOB_PORT \
           --expansion-port 0 \
           --artifact-port 0 &
-      SIMULTANEOUS=1  # Spark runner fails if jobs are run concurrently.
     elif [[ "$RUNNER" == "portable" ]]; then
       python3 \
           -m apache_beam.runners.portability.local_job_service_main \
@@ -305,6 +302,11 @@ elif [[ "$RUNNER" == "flink" || "$RUNNER" == "spark" || "$RUNNER" == "samza" ||
   fi
 fi
 
+# Disable parallelism on runners that don't support it.
+if [[ "$RUNNER" == "flink" || "$RUNNER" == "spark" || "$RUNNER" == "samza" ]]; then
+  SIMULTANEOUS=1
+fi
+
 if [[ "$RUNNER" == "dataflow" ]]; then
   # Verify docker and gcloud commands exist
   command -v docker