Fix average test data

tests/ImageSharp.Tests/Formats/Png/PngDecoderFilterTests.cs

@@ -7,6 +7,7 @@ using Xunit;
 
 namespace SixLabors.ImageSharp.Tests.Formats.Png
 {
+    [Trait("Format", "Png")]
     public class PngDecoderFilterTests
     {
         private static void RunAverageFilterTest()
@@ -18,7 +19,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Png
                 0, 2, 2, 2, 0, 3, 3, 3, 0, 1, 1, 1, 0, 3, 3, 3, 0, 3, 3, 3, 0, 1, 1, 1, 0, 3, 3, 3, 0, 2, 2, 2, 0,
                 1, 1, 1, 0, 3, 3, 3, 0, 1, 1, 1, 0, 3, 3, 3, 0, 1, 1, 1, 0, 3, 3, 3, 0, 3, 3, 3, 0, 254, 254, 254,
                 0, 6, 6, 6, 14, 71, 71, 71, 157, 254, 254, 254, 28, 251, 251, 251, 0, 4, 4, 4, 0, 2, 2, 2, 0, 11,
-                11, 11, 0, 226, 226, 226, 0, 255
+                11, 11, 0, 226, 226, 226, 0, 255, 128, 234
             };
 
             byte[] previousScanline =
@@ -28,7 +29,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Png
                 74, 74, 0, 72, 72, 72, 0, 73, 73, 73, 0, 75, 75, 75, 0, 73, 73, 73, 0, 74, 74, 74, 0, 72, 72, 72, 0,
                 73, 73, 73, 0, 73, 73, 73, 0, 72, 72, 72, 0, 74, 74, 74, 0, 61, 61, 61, 0, 101, 101, 101, 78, 197,
                 197, 197, 251, 152, 152, 152, 255, 155, 155, 155, 255, 162, 162, 162, 255, 175, 175, 175, 255, 160,
-                160, 160, 255, 139
+                160, 160, 255, 139, 128, 134
             };
 
             byte[] expected =
@@ -38,7 +39,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Png
                 76, 76, 0, 77, 77, 77, 0, 77, 77, 77, 0, 77, 77, 77, 0, 78, 78, 78, 0, 77, 77, 77, 0, 77, 77, 77, 0,
                 76, 76, 76, 0, 77, 77, 77, 0, 77, 77, 77, 0, 73, 73, 73, 0, 73, 73, 73, 14, 158, 158, 158, 203, 175,
                 175, 175, 255, 158, 158, 158, 255, 160, 160, 160, 255, 163, 163, 163, 255, 180, 180, 180, 255, 140,
-                140, 140, 255, 255
+                140, 140, 255, 138, 6, 115
             };
 
             // act