The placement-rules and max-replicas are not synchronized.

## Bug Report

### What did you do?

* update default placement-rules `Count`

### What did you expect to see?

```
» config placement-rules show
[
{
"group_id": "pd",
"id": "default",
"start_key": "",
"end_key": "",
"role": "voter",
"is_witness": false,
"count": 1,
"version": 1
}
]
» config show replication
{
"max-replicas": 1,
"location-labels": "",
"strictly-match-label": "false",
"enable-placement-rules": "true",
"enable-placement-rules-cache": "false",
"isolation-level": ""
}
```

### What did you see instead?

```
» config show replication
{
"max-replicas": 2,
"location-labels": "",
"strictly-match-label": "false",
"enable-placement-rules": "true",
"enable-placement-rules-cache": "false",
"isolation-level": ""
}
```

### What version of PD are you using (`pd-server -V`)?

v8.5.3