MessagesTests: allow postpone/suspended in BatchedMessages WaitForCompletion

The old hand-rolled QueueManager in this test used
MessagesDefaultMaxWaitForCompletion = TimeSpan.FromMinutes(1), which
made the in-memory wait long enough that the flow never actually
suspended -- so its WaitForCompletion (defaulting to
allowPostponeAndSuspended: false) was fine.

After switching to workflow.Message<string>(), the framework's
QueueManager runs with MaxWait = TimeSpan.Zero, so the flow does
transition through Postponed (Expires=0 once AppendMessage's
store-level Interrupt fires) before the watchdog re-invokes and the
flow Succeeds. WaitForCompletion was polling during that brief
Postponed window and throwing InvocationPostponedException.

Matches the pattern already used by PingPong and MultipleMessages.

Author: stidsborg

Core/Cleipnir.ResilientFunctions.Tests/Messaging/TestTemplates/MessagesTests.cs

@@ -256,8 +256,8 @@ await registration.SendMessages(
         var controlPanel1 = await registration.ControlPanel("Instance#1").ShouldNotBeNullAsync();
         var controlPanel2 = await registration.ControlPanel("Instance#2").ShouldNotBeNullAsync();
 
-        await controlPanel1.WaitForCompletion(maxWait: TimeSpan.FromSeconds(2));
-        await controlPanel2.WaitForCompletion(maxWait: TimeSpan.FromSeconds(2));
+        await controlPanel1.WaitForCompletion(allowPostponeAndSuspended: true, maxWait: TimeSpan.FromSeconds(2));
+        await controlPanel2.WaitForCompletion(allowPostponeAndSuspended: true, maxWait: TimeSpan.FromSeconds(2));
 
         unhandledExceptionCatcher.ShouldNotHaveExceptions();
     }