Fix warnings (#24)

Author: jeremy-visionaid

samples/Plugin.Maui.KeyListener.Sample/App.xaml.cs

@@ -6,6 +6,11 @@ public App()
 	{
 		InitializeComponent();
 
-		MainPage = new AppShell();
+	}
+
+	protected override Window CreateWindow(IActivationState activationState)
+	{
+		var shell = new AppShell();
+		return new Window(shell);
 	}
 }

samples/Plugin.Maui.KeyListener.Sample/MainPage.xaml.cs

@@ -11,7 +11,7 @@ public MainPage()
 		AddKeyboardBehavior();
 	}
 
-	async void AddKeyboardBehavior()
+	void AddKeyboardBehavior()
 	{
 		var keyboardBehavior = new KeyboardBehavior();
 		keyboardBehavior.KeyDown += (sender, args) => PrependOutput("KeyDown", args);