[Stream] Stream cancellation/completion signal might not reach ActorRefSourceActor

[Arkatufus]

Version Information
Version of Akka.NET? 1.5.18
Which Akka.NET Modules? Akka.Streams

Describe the bug
There is a tentative evidence that stream completion/cancellation signals did not get propagated properly to the ActorRefSourceActor and can lead to memory leak. This might be the ultimate cause of Petabridge.Cmd remote client memory leak issue, the current hotfix for this is here: https://github.com/petabridge/petabridge.cmd/pull/700