nacos配置系统规则后,限流不生效

## Issue Description

Type: *bug report* or *feature request*

### Describe what happened (or what feature you want)
nacos配置规则同步到sentinel dashboard 并未生效

### Describe what you expected to happen
系统规则生效,限流 成功

### How to reproduce it (as minimally and precisely as possible)

1. 在nacos配置界面修改系统规则:
`[
{
"highestSystemLoad": -1,
"avgRt": -1,
"maxThread": -1,
"qps": 30
}
]`
2. sentinel dashboard能看到规则已变化,但是限流并未生效
3. jmeter模拟100个线程,全部成功

### Tell us your environment
```

com.alibaba.cloud
spring-cloud-starter-alibaba-sentinel
2.1.2.RELEASE


com.alibaba.cloud
spring-cloud-starter-alibaba-nacos-discovery
2.1.2.RELEASE


com.alibaba.cloud
spring-cloud-starter-alibaba-nacos-config
2.1.2.RELEASE


com.alibaba.csp
sentinel-datasource-nacos
1.7.2

```

### Anything else we need to know?

Start with the shown Nacos configuration and the sentinel-datasource-nacos 1.7.2 integration, reproducing through Sentinel Dashboard with the listed Spring Cloud Alibaba versions and JMeter load. Done means the dashboard rule is synchronized and a 30-QPS system rule rejects excess requests instead of allowing all 100 threads to succeed.

Written by the indexing model from the issue text.