[BUG] Grouping alerts would replicate one without custom labels.

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Current Behavior

When using grouping, there may be throws multiple alerts in one incident.
like this image.

if I group alerts with custom labels, the label would not be assigned to some alerts. That can cause grouping failed and send so many noisy messages if we have notification rules.

### Expected Behavior

When using grouping, there should be only one alert in one incident. This helps prevent receiving a large number of duplicate alert messages.

### Steps To Reproduce

1. Add some alerts with the same custom label.
2. Add grouping rule with the custom label.
3. Add threshold as normal.
4. Trigger the alart.
5. Turn to alarms page, then we can find multiple alerts here.

### Environment

```markdown
HertzBeat version(s):
```

### Debug logs

_No response_

### Anything else?

_No response_