False positive for `no-invalid-position-declaration` inside a mixin

[Vinnl]

We have the following in our code, which used to be fine, but now gets flagged for no-invalid-position-declaration after updating to the latest versions:

@mixin company-name-area {
  @media screen and (min-width: $screen-lg) {
    min-width: 200px;
  }
}

As far as I can see this should be valid (though admittedly, I haven't really used SCSS mixins myself before). It looks similar to #364.

[jrmlt]

I'll propose a PR after stylelint/stylelint#8781 is merged.