Fix #23737: Update superCallContext to include dummy capture parameters in scope

[noti0na1]

Fix #23737

[natsukagami]

Would be nice to also include a test like this, to ensure that the subtyping relationship works

import language.experimental.captureChecking

class C

trait A[T]

trait B[Cap^] extends A[C^{Cap}]

def f(c: C^) =
  val b = new B[{c}] {}
  val a: A[C^{c}] = b

[odersky]

The logic looks good to me.