Fix chunk type unit tests

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

@@ -32,7 +32,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Png
             Assert.Equal(PngChunkType.SignificantBits, GetType("sBIT"));
             Assert.Equal(PngChunkType.Histogram, GetType("hIST"));
             Assert.Equal(PngChunkType.SuggestedPalette, GetType("sPLT"));
-            Assert.Equal(PngChunkType.MalformedApple, GetType("CgBI"));
+            Assert.Equal(PngChunkType.ProprietaryApple, GetType("CgBI"));
         }
 
         private static PngChunkType GetType(string text)

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

@@ -387,7 +387,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Png
                     }
                 });
             Assert.NotNull(ex);
-            Assert.Contains("Malformed Apple PNG detected!", ex.Message);
+            Assert.Contains("Proprietary Apple PNG detected!", ex.Message);
         }
 
         [Theory]