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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)



return instance;
    }
    private NacosServiceName createServiceName(URL url) {
        return valueOf(url);
    }
    private String getServiceName(URL url) {
        return getServiceName(url, url.getCategory(DEFAULT_CATEGORY));
    }
    private String getServiceName(URL url, String category) {
        return category + SERVICE_NAME_SEPARATOR + url.getColonSeparatedKey();
    }
    private void filterEnabledInstances(Collection<Instance> instances) {
        filterData(instances, Instance::isEnabled);
    }
    /**
     * A filter for Nacos data
     *
     * @since 2.6.5
     */
    private interface NacosDataFilter<T> {
        /**
         * Tests whether or not the specified data should be accepted.
         *
         * @param data The data to be tested
         * @return <code>true</code> if and only if <code>data</code>
         * should be accepted
         */
        boolean accept(T data);
    }
    private class RegistryChildListenerImpl implements EventListener {