[Bug] Type Unsoundness for the schema index signature.

[Peefy]

For the following code, it is expected to get a evaluation error for the type attribute, because it is required.

schema Application:
    name: str
    components: WithComponents

schema WithComponent:
    name: str
    $type: str

schema WithComponents:
    [name: str]: WithComponent = {name: name}

myapp2: Application {
    name: "myapp2"
    components.ws: WithComponent {}
}

But, I've got the YAML output

Related discussion: https://github.com/orgs/kcl-lang/discussions/1005