Fix skia OpacityMask push and pop methods

src/Skia/Avalonia.Skia/DrawingContextImpl.cs

@@ -534,7 +534,11 @@ namespace Avalonia.Skia
         public void PushOpacityMask(IBrush mask, Rect bounds)
         {
             // TODO: This should be disposed
-            var paint = new SKPaint();
+            var paint = new SKPaint()
+            {
+                IsAntialias = true,
+                Style = SKPaintStyle.StrokeAndFill
+            };
 
             Canvas.SaveLayer(paint);
             _maskStack.Push(CreatePaint(paint, mask, bounds, true));
@@ -543,7 +547,14 @@ namespace Avalonia.Skia
         /// <inheritdoc />
         public void PopOpacityMask()
         {
-            using (var paint = new SKPaint { BlendMode = SKBlendMode.DstIn })
+            using (var paint = new SKPaint
+            {
+                IsAntialias = true,
+                Style = SKPaintStyle.StrokeAndFill,
+                BlendMode = SKBlendMode.DstIn,
+                Color = new SKColor(0, 0, 0, 255),
+                ColorFilter = SKColorFilter.CreateLumaColor()
+            })
             {
                 Canvas.SaveLayer(paint);
                 using (var paintWrapper = _maskStack.Pop())