SemaphoreStep.onResume needs to add the key to State.started

Author: dwnusbaum

src/test/java/org/jenkinsci/plugins/workflow/test/steps/SemaphoreStep.java

@@ -246,6 +246,7 @@ public static class Execution extends AbstractStepExecutionImpl {
                 } else {
                     s.contexts.put(k, c);
                 }
+                s.started.add(k);
                 s.notifyAll();
             }
         }