Speedup HealthNodeTaskExecutor CS listener

This method was quite slow in tests because there's an expensive
assertion in `ClusterApplierService.state()` that we run when calling
`ClusterService.localNode()`

server/src/main/java/org/elasticsearch/health/node/selection/HealthNodeTaskExecutor.java

@@ -186,8 +186,8 @@ void startTask(ClusterChangedEvent event) {
 
  // visible for testing
  void shuttingDown(ClusterChangedEvent event) {
- DiscoveryNode node = clusterService.localNode();
- if (isNodeShuttingDown(event, node.getId())) {
+ if (isNodeShuttingDown(event)) {
+  var node = event.state().getNodes().getLocalNode();
  abortTaskIfApplicable("node [{" + node.getName() + "}{" + node.getId() + "}] shutting down");
  }
  }
@@ -202,9 +202,18 @@ void abortTaskIfApplicable(String reason) {
  }
  }
 
- private static boolean isNodeShuttingDown(ClusterChangedEvent event, String nodeId) {
- return event.previousState().metadata().nodeShutdowns().contains(nodeId) == false
- && event.state().metadata().nodeShutdowns().contains(nodeId);
+ private static boolean isNodeShuttingDown(ClusterChangedEvent event) {
+ if (event.metadataChanged() == false) {
+ return false;
+ }
+ var shutdownsOld = event.previousState().metadata().nodeShutdowns();
+ var shutdownsNew = event.state().metadata().nodeShutdowns();
+ if (shutdownsNew == shutdownsOld) {
+ return false;
+ }
+ String nodeId = event.state().nodes().getLocalNodeId();
+ return shutdownsOld.contains(nodeId) == false && shutdownsNew.contains(nodeId);
+
  }
 
  public static List<NamedXContentRegistry.Entry> getNamedXContentParsers() {