[Bug] when pie legend icon="circle", series itemStyle influence it's size.

### Version

5.1.0.0-current

### Link to Minimal Reproduction

without

### Steps to Reproduce

``

ECharts 饼图示例

var myChart = echarts.init(document.getElementById('main'));

var option = {
title: {
text: '访问来源',
left: 'center'
},
legend: {
icon: 'circle',
itemWidth: 8
},
tooltip: {
trigger: 'item',
formatter: '{a} <br/>{b} : {c} ({d}%)'
},
series: [
{
name: '访问来源',
type: 'pie',
radius: '50%',
data: [
{value: 1048, name: '搜索引擎'},
{value: 735, name: '直接访问'},
{value: 580, name: '邮件营销'},
{value: 484, name: '联盟广告'},
{value: 300, name: '视频广告'}
],
emphasis: {
itemStyle: {
shadowBlur: 10,
shadowOffsetX: 0,
shadowColor: 'rgba(0, 0, 0, 0.5)'
}
},
itemStyle: {
borderWidth: 1,
borderColor: '#ffffff'
},
label: {
show: true,
color: 'inherit'
}
}
]
};

myChart.setOption(option);

`
`

### Current Behavior

when pie legend icon="circle", series itemStyle influence it's size.

### Expected Behavior

legend icon size keep it the same

### Environment

```markdown
OS: macOS Monterey
Browser: Chrome 96.0.4664.55
Framework Vue
```

### Any additional comments?

_No response_