Compare image on windows only for now.

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

@@ -92,10 +92,14 @@ namespace SixLabors.ImageSharp.Tests.Formats.Png
             {
                 image.DebugSave(provider);
 
+                // We don't have another x-plat reference decoder that can be compared for this image.
                 if (provider.Utility.SourceFileOrDescription == TestImages.Png.Bad.Issue1047_BadEndChunk)
+                {
+                    if (TestEnvironment.IsWindows)
                     {
                         image.CompareToOriginal(provider, ImageComparer.Exact, (IImageDecoder)SystemDrawingReferenceDecoder.Instance);
                     }
+                }
                 else
                 {
                     image.CompareToOriginal(provider, ImageComparer.Exact);