chore: Adjust Width of TextBox for test

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Controls/Given_TextBox.skia.cs

@@ -764,7 +764,7 @@ public async Task When_Scrolling_Updates_With_Movement()
 
 			var SUT = new TextBox
 			{
-				Width = 40,
+				Width = 64, // == TextControlThemeMinWidth for UWP styles
 				Text = "This should be a lot longer than the width of the TextBox."
 			};