[CmdPal] Fix correct comment typo in SamplePagesExtension (#40242)

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## Summary of the Pull Request

Fixed a simple English grammar error in SamplePagesExtension in CmdPal.

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Author: purofle

src/modules/cmdpal/ext/SamplePagesExtension/Program.cs

@@ -25,7 +25,7 @@ public static void Main(string[] args)
             server.RegisterExtension(() => extensionInstance);
 
             // This will make the main thread wait until the event is signalled by the extension class.
-            // Since we have single instance of the extension object, we exit as soon as it is disposed.
+            // Since we have a single instance of the extension object, we exit as soon as it is disposed.
             extensionDisposedEvent.WaitOne();
         }
         else