Incorrect parameterized typecheck

This code:

```pkl
class Foo { bar: Int }
const function isOk(f: Foo) = f.bar > 0
typealias T<X> = Int(isOk(new { bar = 1 }) && this is X)

res = 3 is T<String>
```

Gives

```
res = true
```

But should be:

```
res = false
```