### Environment

* Dubbo version: 3.0
StaticDirectory.destroy方法最后要对列表做clear操作，但是ReferenceConfig的createInvokerForLocal构造StaticDirectory传入的列表类型是Collections.singletonList，执行clear就会抛异常：
```
[08/10/21 07:35:39:302 UTC] main  WARN config.ReferenceConfig:  [DUBBO] Unexpected error occurred when destroy invoker of ReferenceConfig(null)., dubbo version: 3.0.4-SNAPSHOT, current host: 172.19.112.1
java.lang.UnsupportedOperationException
	at java.util.AbstractList.remove(AbstractList.java:161)
	at java.util.AbstractList$Itr.remove(AbstractList.java:374)
	at java.util.AbstractList.removeRange(AbstractList.java:571)
	at java.util.AbstractList.clear(AbstractList.java:234)
	at org.apache.dubbo.rpc.cluster.directory.StaticDirectory.destroy(StaticDirectory.java:91)
	at org.apache.dubbo.rpc.cluster.support.AbstractClusterInvoker.destroy(AbstractClusterInvoker.java:113)
	at org.apache.dubbo.rpc.cluster.support.wrapper.MockClusterInvoker.destroy(MockClusterInvoker.java:79)
	at org.apache.dubbo.config.ReferenceConfig.destroy(ReferenceConfig.java:219)
```
return services;
    }
    /**
     * It's an alias method for {@link #getServices()}, but the more convenient.
     *
     * @return the String {@link List} presenting the Dubbo interface subscribed
     * @since 2.7.8
     */
    @Deprecated
    @Parameter(excluded = true)
    public Set<String> getSubscribedServices() {
        return splitToSet(getServices(), COMMA_SEPARATOR_CHAR);
    }
    /**
     * Set the service names that the Dubbo interface subscribed.
     *
     * @param services If it is a multiple-values, the content will be a comma-delimited String.
     * @since 2.7.8
     */
    public void setServices(String services) {
        this.services = services;
    }
    @Override
    public synchronized T get() {
        if (destroyed) {
            throw new IllegalStateException("The invoker of ReferenceConfig(" + url + ") has already destroyed!");
        }
        if (ref == null) {
            init();
        }