Fix flaky test ExecuteAsync_WhenStepFails_PipelineLoggerIsCleanedUp (#12341)

* Initial plan

* Fix race condition in pipeline step activity reporting

Use CancellationToken.None when creating step activities to prevent race condition where a failing step could cancel the token before other concurrent steps finish creating their activities.

Co-authored-by: davidfowl <95136+davidfowl@users.noreply.github.com>

* Revert pipeline change and fix test to only verify failing step

Reverted the CancellationToken.None change to preserve fail-fast behavior as requested by @davidfowl. Updated the test to focus on verifying the single failing step rather than asserting an exact count of step activities, making it more resilient to timing variations while maintaining fail-fast behavior.

Co-authored-by: davidfowl <95136+davidfowl@users.noreply.github.com>

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: davidfowl <95136+davidfowl@users.noreply.github.com>

Author: 2 people

tests/Aspire.Hosting.Tests/Pipelines/DistributedApplicationPipelineTests.cs

@@ -1526,11 +1526,8 @@ public async Task ExecuteAsync_WhenStepFails_PipelineLoggerIsCleanedUp()
         var stepActivities = activities.Where(a => a.Type == PublishingActivityTypes.Step).GroupBy(a => a.Data.Id).ToList();
         var logActivities = activities.Where(a => a.Type == PublishingActivityTypes.Log).ToList();
 
-        Assert.Equal(2, stepActivities.Count); // Updated to account for "deploy" step
-        
-        // Find the failing-step activity
-        var failingStepActivity = stepActivities.FirstOrDefault(g => g.Any(a => a.Data.StatusText == "failing-step"));
-        Assert.NotNull(failingStepActivity);
+        // Verify the failing step activity (other steps may or may not complete depending on timing)
+        var failingStepActivity = stepActivities.Single(g => g.Any(a => a.Data.StatusText == "failing-step"));
         Assert.Collection(failingStepActivity,
             step =>
             {