Remove unnecessary SendAppearing call (#22959)

### Description of Change

PopLifeCycle occasionally fails in CI and we'll see if it's caused by
this extra call

src/Controls/tests/Core.UnitTests/NavigationPageLifecycleTests.cs

@@ -81,7 +81,6 @@ void OnInitialPageAppearing(object sender, EventArgs e)
 
 			_ = new TestWindow(nav);
 
-			nav.SendAppearing();
 			await waitForFirstAppearing.Task;
 			initialPage.Appearing += (sender, _)
 				=> rootPageFiresAppearingAfterPop = (ContentPage)sender;