It is supposed to log with warn-level instead of info-level

## Issue Description

### Describe what happened (or what feature you want)

```java
if (flushInterval <= 0) {
RecordLog.info("[FlowRuleManager] The MetricTimerListener isn't started. If you want to start it, "
+ "please change the value(current: {}) of config({}) more than 0 to start it.", flushInterval,
SentinelConfig.METRIC_FLUSH_INTERVAL);
return;
}
```
it is logging with info-level.

### Describe what you expected to happen

There should log with warn-level because if `flushInterval <= 0` there should be a warning.

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

1.
2.
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### Tell us your environment

### Anything else we need to know?

Start from the FlowRuleManager MetricTimerListener code shown in the issue and inspect the branch where flushInterval is less than or equal to zero. Change the reported log severity to warn-level, then verify that this branch emits a warning with the existing message and arguments.

Written by the indexing model from the issue text.