Random occasional `SubscriptionWithCancelException$NoMoreElementsNeeded` after migrating from Akka to Pekko

Hey, I notice that when I migrate to Pekko (form latest "free" Akka), I start getting occasional `org.apache.pekko.stream.SubscriptionWithCancelException$NoMoreElementsNeeded$ (No error message supplied)` from web clients.

I've increased `stream-cancellation-delay` to `1s` but still it fails sometimes. It does really look like something changed from Akka to Pekko.

I don't really have any code to reproduce as it's not consistent, maybe once in couple of days. But reverting back to Akka does fix it.

Start with the reported SubscriptionWithCancelException$NoMoreElementsNeeded failure in Pekko web clients and compare behavior after migrating from Akka. Check how the stream-cancellation-delay setting affects the failure, using the reported 1s value as a reference. Done means identifying a reproducible regression or a concrete cause for the intermittent cancellation.

Written by the indexing model from the issue text.