fix extra ' in externalizableId test pipeline definition

Author: stuartrowe

src/test/java/org/jenkinsci/plugins/workflow/support/steps/build/RunWrapperTest.java

@@ -292,7 +292,7 @@ public void upstreamBuilds() throws Throwable {
     public void externalizableId() throws Throwable {
         sessions.then(j -> {
             WorkflowJob first = j.createProject(WorkflowJob.class, "first-job");
-            first.setDefinition(new CpsFlowDefinition("echo currentBuild.getExternalizableId()'\n", true));
+            first.setDefinition(new CpsFlowDefinition("echo currentBuild.getExternalizableId()\n", true));
             WorkflowRun firstRun = j.buildAndAssertSuccess(first);
             j.assertLogContains(firstRun.getExternalizableId(), firstRun);
         });