Don't detect rogue OperationCanceledException as ctrl+c. (#3272)

Author: timcassell

src/BenchmarkDotNet/Helpers/CtrlCCanceler.cs

@@ -8,6 +8,8 @@ internal sealed class CtrlCCanceler : IDisposable
         private readonly CancellationTokenSource cts;
         private readonly ILogger logger;
 
+        public bool IsCancelled => Volatile.Read(ref cancelled) == 1;
+
         private CtrlCCanceler(CancellationTokenSource cts, ILogger logger)
         {
             this.logger = logger;