Update Listing04.39.Tests.cs

Co-authored-by: Kevin B <[email protected]>

src/Chapter04.Tests/Listing04.39.Tests.cs

@@ -20,7 +20,7 @@ public void ChangeTemperatureWithoutConditionalOperator()
     public void ChangeHumidityWithConditionalOperator()
     {
         bool eventFired = false;
-        Person thermostat = new();
+        Person person= new();
         thermostat.PropertyChanged += (object? sender, EventArgs e) =>
         {
             eventFired = true;