[Bug] "DEPRECATED: "api.style" has been deprecated"

### Version

5.2.2

### Link to Minimal Reproduction

https://echarts.apache.org/examples/en/editor.html?c=custom-polar-heatmap

### Steps to Reproduce

1. Open https://echarts.apache.org/examples/en/editor.html?c=custom-polar-heatmap

### Current Behavior

An option from the doc is deprecated

### Expected Behavior

The options from the docs shouldn't be deprecated

### Environment

```markdown
- OS: Windows
- Browser: Chrome
- Framework: /
```

### Any additional comments?

I am using this echarts from example in my app : https://echarts.apache.org/examples/en/editor.html?c=custom-polar-heatmap
However, I have this warn in the console : `styleCompat.js:238 [ECharts] DEPRECATED: "api.style" has been deprecated. Please write literal style directly instead.`
I tried to find more about it and I could only find a bit of info in the Echarts changelog `In renderItem, the api.style(...) and api.styleEmphasis(...) are deprecated. Because it is not really necessary and hard to ensure backward compatibility. Users can fetch system designated visual by api.visual(...).`
Though, I couldn't find more and the doc still make the use of `api.style()` : https://echarts.apache.org/en/option.html#series-custom.renderItem.return

What should I change in the example above to make it works without deprecacted options ?

Start with the linked custom-polar-heatmap reproduction and compare its renderItem usage with the renderItem return documentation linked in the issue. Locate the example and documentation source that produce the warning, then verify that the example works without the deprecated option and no longer logs the deprecation message.

Written by the indexing model from the issue text.