fix center snap alignment

samples/ControlCatalog/Pages/ScrollSnapPage.xaml.cs

@@ -50,6 +50,7 @@ namespace ControlCatalog.Pages
         public List<SnapPointsType> AvailableSnapPointsType { get; }
         public List<SnapPointsAlignment> AvailableSnapPointsAlignment { get; }
     }
+
     public class ScrollSnapPage : UserControl
     {
         public ScrollSnapPage()

src/Avalonia.Controls/Presenters/ScrollContentPresenter.cs

@@ -869,7 +869,7 @@ namespace Avalonia.Controls.Presenters
 
                 if (!_areVerticalSnapPointsRegular)
                 {
-                    _verticalSnapPoints = scrollSnapPointsInfo.GetIrregularSnapPoints(Layout.Orientation.Vertical, HorizontalSnapPointsAlignment);
+                    _verticalSnapPoints = scrollSnapPointsInfo.GetIrregularSnapPoints(Layout.Orientation.Vertical, VerticalSnapPointsAlignment);
                 }
                 else
                 {