append does not dispose the second signal

[ioninks]

Consider the following example:

let periodic = SafeSignal<Int>(sequence: 0..., interval: 1.0)
  .map(String.init)
  .debug("periodic")

let initial = SafeSignal(just: "0")

initial.append(periodic)
  .prefix(maxLength: 3)
  .debug("final")
  .observeNext { _ in }
  .dispose(in: bag)

If we run it, here is what will be printed out:

[final] started
[final] next(0)
[periodic] started
[periodic] next(0)
[final] next(0)
[periodic] next(1)
[final] next(1)
[final] finished
[final] disposed
[periodic] next(2)
[periodic] next(3)
[periodic] next(4)
[periodic] next(5)
...

So as you can see the periodic signal was not disposed and keeps producing elements.

Furthermore, if we replace append(periodic) with merge(with: periodic) it is disposed correctly:

[final] started
[final] next(0)
[periodic] started
[periodic] next(0)
[final] next(0)
[periodic] next(1)
[final] next(1)
[periodic] disposed
[final] finished
[final] disposed