### Environment

* Dubbo version: dubbo-registry-nacos 2.7.6
* Operating System version: Win10
* Java version: JAVA 8

### Steps to reproduce this issue
1 springboot  yml配置如下： 
registry:
     address: nacos://127.0.0.1:8848
     simplified: true
     group: dubbo-local
  metadata-report:
            address: nacos://127.0.0.1:8848
            group: dubbo-local

2 登陆nacos 1.2.1 控制台发现元数据 group配置生效，但是服务管理下的group依旧是DEFAULT_GROUP。

3 跟了下dubbo-registry-nacos 2.7.6的代码 发现在调用NamingService中 没有传入配置的group参数，使用的默认组参数 
 public void doRegister(URL url) {
        String serviceName = this.getServiceName(url);
        Instance instance = this.createInstance(url);
        this.execute((namingService) -> {
            namingService.registerInstance(serviceName, instance);
        });
    }

Pls. provide [GitHub address] to reproduce this issue.

### Expected Result

What do you expected from the above steps？

### Actual Result

What actually happens?

If there is an exception, please attach the exception trace:

```
Just put your stack trace here!
```

private static final long LOOKUP_INTERVAL = Long.getLong("nacos.service.names.lookup.interval", 30);
    /**
     * {@link ScheduledExecutorService} lookup Nacos service names(only for Dubbo-OPS)
     */
    private volatile ScheduledExecutorService scheduledExecutorService;
    private final Logger logger = LoggerFactory.getLogger(getClass());
    private final NamingService namingService;
    public NacosRegistry(URL url, NamingService namingService) {
        super(url);
        this.namingService = namingService;
    }
    @Override
    public boolean isAvailable() {
        return "UP".equals(namingService.getServerStatus());
    }
    @Override
    public List<URL> lookup(final URL url) {
        final List<URL> urls = new LinkedList<>();
        execute(namingService -> {
            Set<String> serviceNames = getServiceNames(url, null);
            for (String serviceName : serviceNames) {
                List<Instance> instances = namingService.getAllInstances(serviceName);
                urls.addAll(buildURLs(url, instances));
            }
        });
        return urls;
    }
    @Override
    public void doRegister(URL url) {
        final String serviceName = getServiceName(url);