Reduce memory pressure on gif decoder tests

tests/ImageSharp.Tests/Formats/Gif/GifDecoderTests.cs

@@ -101,9 +101,9 @@ public class GifDecoderTests
     }
 
     [Theory]
-    [WithFile(TestImages.Gif.Cheers, PixelTypes.Rgba32, 93)]
+    [WithFile(TestImages.Gif.M4nb, PixelTypes.Rgba32, 5)]
     [WithFile(TestImages.Gif.Rings, PixelTypes.Rgba32, 1)]
-    [WithFile(TestImages.Gif.Issues.BadDescriptorWidth, PixelTypes.Rgba32, 36)]
+    [WithFile(TestImages.Gif.MixedDisposal, PixelTypes.Rgba32, 11)]
     public void Decode_VerifyRootFrameAndFrameCount<TPixel>(TestImageProvider<TPixel> provider, int expectedFrameCount)
         where TPixel : unmanaged, IPixel<TPixel>
     {

tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_VerifyRootFrameAndFrameCount_Rgba32_cheers.png

@@ -1,3 +0,0 @@
-version https://git-lfs.github.com/spec/v1
-oid sha256:b199a36f9e682a54c5d7c67f3403bba174b37e1a7a8412481f66c6d5eb0349e9
-size 27679

tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_VerifyRootFrameAndFrameCount_Rgba32_issue403_baddescriptorwidth.png

@@ -1,3 +0,0 @@
-version https://git-lfs.github.com/spec/v1
-oid sha256:4bedcf1a0ca0281dd5531d96c74e19c5d5fd379d6e2acb899077299917215705
-size 1013

tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_VerifyRootFrameAndFrameCount_Rgba32_m4nb.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:04239ee46f0276ba52566bcb2407f4a6fcee35b3f51a6182394f851e2d8df3fc
+size 277

tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_VerifyRootFrameAndFrameCount_Rgba32_mixed-disposal.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:0b654f948a26d256ff9e28ada399465bd6a4205aedaf93ea7cdffb70483535ef
+size 2216