[Bug]: indeterminate state for sp-swatch shows an "Elements must only use supported ARIA attributes" error

[Rocss]

Code of conduct

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Impacted component(s)

sp-swatch

Expected behavior

No accessibility warnings should be thrown

Actual behavior

Issue was observed in Express, but it is reproducing on Spectrum Web Components documentation as well: https://opensource.adobe.com/spectrum-web-components/components/swatch/

Screenshots

What browsers are you seeing the problem in?

No response

How can we reproduce this issue?

1. Go to https://opensource.adobe.com/spectrum-web-components/components/swatch/
2. Open the axe-devtools extension and run a full scan of the page
3. Observe the accessibility error: "Ensures an element's role supports its ARIA attributes"

Sample code that illustrates the problem

While aria-checked="mixed" would be useful in a sp-swatch-group where the role of the sp-swatch would be checkbox, in a single sp-swatch which surfaces the role=button, the use of aria-checked is invalid.
The "mixed" state should be part of the aria-label in this case.

Logs taken while reproducing problem

No response