Fix Windows-RabbitMQ RunScenario test timeout and cascade failures (#5456)

GetThroughputPerDay loops 96 times (24*4), each requiring an HTTP call to
the RabbitMQ management API plus sending and receiving 15 messages. On Windows
CI, this consistently exceeds the 60-second TestTimeout that bounds all
CreateTaskCompletionSource instances via testCancellationTokenSource, causing
the test to fail with a timeout error mid-run.

When the timeout fires while the message pump is still running, the subsequent
delivery calls SetResult on an already-faulted TCS, throwing
InvalidOperationException. This propagates through the RabbitMQ pump as a
processing error, triggering the onError Assert.Fail, which then escalates to
the critical-error handler, producing three apparent failures from one root cause.

- Raise TestTimeout from 60s to 5 minutes to accommodate the test's 3-minute
  design budget with margin for slower Windows CI runners
- Change SetResult to TrySetResult to stop the cascade when a concurrent
  timeout and message delivery race

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: mauroservienti

src/ServiceControl.Transports.Tests/TransportTestFixture.cs

@@ -185,7 +185,7 @@ protected Task CreateTestQueue(string queueName)
             return configuration.TransportCustomization.ProvisionQueues(transportSettings, []);
         }
 
-        protected static TimeSpan TestTimeout = TimeSpan.FromSeconds(60);
+        protected static TimeSpan TestTimeout = TimeSpan.FromMinutes(5);
 
         protected async Task SendAndReceiveMessages(string queueName, int numMessagesToIngest)
         {
@@ -200,7 +200,7 @@ await StartQueueIngestor(
 
                     if (numMessagesIngested == numMessagesToIngest)
                     {
-                        onMessagesProcessed.SetResult(true);
+                        onMessagesProcessed.TrySetResult(true);
                     }
 
                     return Task.CompletedTask;