Fix logic error with IsUsable check

We definitely do not want to ignore cancel requests when the
runspace **is** usable. Oops

Author: SeeminglyScience

src/PowerShellEditorServices/Services/PowerShell/Execution/SynchronousPowerShellTask.cs

@@ -333,7 +333,7 @@ private void StopDebuggerIfRemoteDebugSessionFailed()
 
         private void CancelNormalExecution()
         {
-            if (_pwsh.Runspace.RunspaceStateInfo.IsUsable())
+            if (!_pwsh.Runspace.RunspaceStateInfo.IsUsable())
             {
                 return;
             }