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- [x] I have searched the [issues](https://github.com/apache/dubbo/issues) of this repository and believe that this is not a duplicate.

### Environment

* Dubbo version: 2.7.14、3.0.4

### Steps to reproduce this issue

1. start dubbo admin (nacos registry)

The ```EventListener``` instance has created countless times by the scheduled task(```scheduledExecutorService```) and cached in the ```InstancesChangeNotifier#listenerMap```(Nacos)  , until the memory is full.

- NacosRegistry
```
private void subscribeEventListener(String serviceName, final URL url, final NotifyListener listener)
        throws NacosException {
        EventListener eventListener = new RegistryChildListenerImpl(serviceName, url, listener);
        namingService.subscribe(serviceName,
            getUrl().getGroup(Constants.DEFAULT_GROUP),
            eventListener);
}
```

- InstancesChangeNotifier
```
private final Map<String, ConcurrentHashSet<EventListener>> listenerMap = new ConcurrentHashMap<String, ConcurrentHashSet<EventListener>>();

public void registerListener(String serviceName, String clusters, EventListener listener) {
        String key = ServiceInfo.getKey(serviceName, clusters);
        ConcurrentHashSet<EventListener> eventListeners = listenerMap.get(key);
        if (eventListeners == null) {
            synchronized (lock) {
                eventListeners = listenerMap.get(key);
                if (eventListeners == null) {
                    eventListeners = new ConcurrentHashSet<EventListener>();
                    listenerMap.put(key, eventListeners);
                }
            }
        }
        eventListeners.add(listener);
}
```
The ```namingService.subscribe```  is finally called to the ```InstancesChangeNotifier#registerListener``` , so 
eventListener cached in  eventListeners.

![image](https://user-images.githubusercontent.com/5037807/140080041-f617bda2-0f48-4669-8e3d-2184a6eb9a75.png)



* @param url {@link URL}
     * @return non-null array
     */
    private List<String> getCategories(URL url) {
        return ANY_VALUE.equals(url.getServiceInterface()) ?
            ALL_SUPPORTED_CATEGORIES : Arrays.asList(DEFAULT_CATEGORY);
    }
    private URL buildURL(URL consumerURL, Instance instance) {
        Map<String, String> metadata = instance.getMetadata();
        String protocol = metadata.get(PROTOCOL_KEY);
        String path = metadata.get(PATH_KEY);
        URL url = new ServiceConfigURL(protocol,
            instance.getIp(),
            instance.getPort(),
            path,
            instance.getMetadata());
        return new DubboServiceAddressURL(url.getUrlAddress(), url.getUrlParam(), consumerURL, null);
    }
    private Instance createInstance(URL url) {
        
        String category = url.getCategory(DEFAULT_CATEGORY);
        URL newURL = url.addParameter(CATEGORY_KEY, category);
        newURL = newURL.addParameter(PROTOCOL_KEY, url.getProtocol());
        newURL = newURL.addParameter(PATH_KEY, url.getPath());
        String ip = url.getHost();
        int port = url.getPort();
        Instance instance = new Instance();
        instance.setIp(ip);
        instance.setPort(port);
        instance.setMetadata(new HashMap<>(newURL.getParameters()));