Replace test image with a smaller one.

Adjusted Identify_AnimatedPng_ReadsFrameCountCorrectly to expect 48 frames instead of 50.

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

@@ -420,7 +420,7 @@ public partial class PngDecoderTests
         ImageInfo imageInfo = Image.Identify(stream);
 
         Assert.NotNull(imageInfo);
-        Assert.Equal(50, imageInfo.FrameMetadataCollection.Count);
+        Assert.Equal(48, imageInfo.FrameMetadataCollection.Count);
     }
 
     [Theory]

tests/Images/Input/Png/animated/issue-animated-frame-count.png

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:62d51679bcb096ae45ae0f5bf874916ad929014f68ae43b487253d5050c8b68b
-size 13561079
+oid sha256:af4e320f586ab26c55612a7ccfc98a8c99cd6a0efe8a70d379503751d06fe8bd
+size 51542