Fix selector-type-no-unknown false positive for model

[Mouvedia]

What minimal example or steps are needed to reproduce the bug?

model {}

What minimal configuration is needed to reproduce the bug?

{
  "rules": {
    "selector-type-no-unknown": true
  }
}

References

https://developer.apple.com/videos/play/wwdc2023/10279/ @ 13:25
https://immersive-web.github.io/model-element/

Do you have a proposal to fix the bug?

add to https://github.com/stylelint/stylelint/blob/main/lib/reference/selectors.mjs#L39