"stacked" option has no effect on radial axis

### Expected behavior

The [documentation](https://www.chartjs.org/docs/latest/axes/radial/linear.html) says the `stacked` property is available for all axes. When using it on a radar chart, the same behavior is expected as in line charts: the various datasets are stacked. Only, the stacking should happen on the radial axis instead of the y-axis since it's a radar chart.

### Current behavior

Currently, adding `scales: { r: { stacked: true } }` to the options of the radar chart has no effect at all. The datasets are not stacked.

### Reproducible sample

https://codepen.io/jcrejgpdigjijb/pen/poLmeop

### Optional extra steps/info to reproduce

_No response_

### Possible solution

_No response_

### Context

_No response_

### chart.js version

v3.9.1

### Browser name and version

Firefox 103.0.2

### Link to your project

_No response_