Fix EventSourcedBehaviorRetentionSpec non-determinism

Split the second batch of 10 increments into smaller batches (3+3+4)
with intermediate assertions after each batch. This ensures snapshot
and delete signals are observed in the expected order, preventing
flaky test failures caused by interleaving of async operations.

Upstream: akka/akka-core@f38f8cce11
Cherry-picked from akka/akka-core v2.8.0, which is now Apache licensed.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: He-Pin

persistence-typed-tests/src/test/scala/org/apache/pekko/persistence/typed/scaladsl/EventSourcedBehaviorRetentionSpec.scala

@@ -286,13 +286,21 @@ class EventSourcedBehaviorRetentionSpec
       snapshotSignalProbe.expectSnapshotCompleted(9)
       snapshotSignalProbe.expectDeleteSnapshotCompleted(3, 0)
 
-      (1 to 10).foreach(_ => persistentActor ! Increment)
+      (1 to 3).foreach(_ => persistentActor ! Increment)
       persistentActor ! GetValue(replyProbe.ref)
-      replyProbe.expectMessage(State(20, (0 until 20).toVector))
+      replyProbe.expectMessage(State(13, (0 until 13).toVector))
       snapshotSignalProbe.expectSnapshotCompleted(12)
       snapshotSignalProbe.expectDeleteSnapshotCompleted(6, 0)
+
+      (1 to 3).foreach(_ => persistentActor ! Increment)
+      persistentActor ! GetValue(replyProbe.ref)
+      replyProbe.expectMessage(State(16, (0 until 16).toVector))
       snapshotSignalProbe.expectSnapshotCompleted(15)
       snapshotSignalProbe.expectDeleteSnapshotCompleted(9, 3)
+
+      (1 to 4).foreach(_ => persistentActor ! Increment)
+      persistentActor ! GetValue(replyProbe.ref)
+      replyProbe.expectMessage(State(20, (0 until 20).toVector))
       snapshotSignalProbe.expectSnapshotCompleted(18)
       snapshotSignalProbe.expectDeleteSnapshotCompleted(12, 6)