Treemap rich label alignment issue in echarts 5

### Version
5.0.1

### Steps to reproduce
1. Open Treemap example (https://echarts.apache.org/examples/en/editor.html?c=treemap-disk)
2. Add the following label configuration:
```js
// option.series ...
label: {
show: true,
formatter: (x) => `{blue|${x.name}}`,
rich: {
blue: {
color: "blue"
}
}
}
// ...
```
3. Notice labels are aligned in top left corner while they should be centered

### What is expected?
Labels are centered (except when configured otherwise)

### What is actually happening?
Labels are in top left corner


---
Running the exact same code in the treemap demo of echarts 4 (https://echarts.apache.org/v4/examples/en/editor.html?c=treemap-disk) does not have this issue.


Also, explicitly setting `align: "center", verticalAlign: "middle"` does not help; the label will get centered horizontally, but _not_ vertically.