test: stabilize summary retry background wait

MeetingAssistant.Tests/MeetingSummaryRetryRunnerTests.cs

@@ -189,7 +189,9 @@ public sealed class MeetingSummaryRetryRunnerTests
                     return;
                 }
 
-                await stateChanged.Task.WaitAsync(TimeSpan.FromMilliseconds(100));
+                await Task.WhenAny(
+                    stateChanged.Task,
+                    Task.Delay(TimeSpan.FromMilliseconds(100)));
             }
 
             throw new TimeoutException($"Expected {count} state changes.");