Fix GETSET benchmark

Former-commit-id: 59173a2ea1f93e0b84a7ca026d572a721a166b5f
Former-commit-id: 2174f77edb68a8c348b20b34e9e0046f3a9eae69
Former-commit-id: 238d14a0644251f40dc75f8cd10f98e4d5ed94cc

tests/ImageProcessorCore.Benchmarks/Image/GetSetPixel.cs

@@ -26,7 +26,7 @@
             CoreImage image = new CoreImage(400, 400);
             using (IPixelAccessor<CoreColor, uint> imagePixels = image.Lock())
             {
-                imagePixels[200, 200] = new CoreColor(255, 255, 255, 255);
+                imagePixels[200, 200] = CoreColor.White;
                 return imagePixels[200, 200];
             }
         }