properly canceling StartupOperation (#11318)

Author: brettsam

src/WebJobs.Script.WebHost/WebJobsScriptHostService.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the MIT License. See License.txt in the project root for license information.
 
 using System;
@@ -317,7 +317,7 @@ private async Task StartHostAsync(CancellationToken cancellationToken, int attem
                 }
                 finally
                 {
-                    activeOperation.Dispose();
+                    EndStartupOperation(activeOperation);
                     _hostStartSemaphore.Release();
                 }
             }