fix race conditions with ReceivePersistentActorTests (#7194)

Subscriptions to the `EventStream` need to happen _before_ the actor emitting events starts, otherwise we can end up in a scenario where everything works but the assertion fails.

src/core/Akka.Persistence.Tests/ReceivePersistentActorTests.cs

@@ -31,9 +31,9 @@ public void Given_persistent_actor_with_no_receive_command_specified_When_receiv
             //Given
             var pid = "p-1";
             WriteEvents(pid, 1, 2, 3);
-            var actor = Sys.ActorOf(Props.Create(() => new NoCommandActor(pid)), "no-receive-specified");
             Sys.EventStream.Subscribe(TestActor, typeof(UnhandledMessage));
-
+            var actor = Sys.ActorOf(Props.Create(() => new NoCommandActor(pid)), "no-receive-specified");
+
             //When
             actor.Tell("Something");
 
@@ -50,8 +50,8 @@ public void Given_persistent_actor_with_no_receive_event_specified_When_receivin
             WriteEvents(pid, "Something");
 
             // when
-            var actor = Sys.ActorOf(Props.Create(() => new NoEventActor(pid)), "no-receive-specified");
             Sys.EventStream.Subscribe(TestActor, typeof(UnhandledMessage));
+            var actor = Sys.ActorOf(Props.Create(() => new NoEventActor(pid)), "no-receive-specified");
 
             //Then
             ExpectMsg<UnhandledMessage>(m => ((string)m.Message) == "Something" && Equals(m.Recipient, actor));