Scope leak check produces false positive when using type lambda in a private type alias

[nigredo-tori]

reproduction steps

Using Scala 2.13.5,

object foo {
  private class Bar
  // error: private class Bar escapes its defining scope as part of type foo.this.Bar
  private type Baz = ({ type X = Bar})#X
}

problem

Baz is private, so Bar does not escape its defining scope.