Add test for gray tiff jpeg compressed

tests/ImageSharp.Tests/Formats/Tiff/TiffDecoderTests.cs

@@ -370,6 +370,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
         [WithFile(RgbWithStripsJpegCompressed, PixelTypes.Rgba32)]
         [WithFile(YCbCrJpegCompressed, PixelTypes.Rgba32)]
         [WithFile(RgbJpegCompressedNoJpegTable, PixelTypes.Rgba32)]
+        [WithFile(GrayscaleJpegCompressed, PixelTypes.Rgba32)]
         public void TiffDecoder_CanDecode_JpegCompressed<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : unmanaged, IPixel<TPixel> => TestTiffDecoder(provider, useExactComparer: false);
 

tests/ImageSharp.Tests/TestImages.cs

@@ -772,6 +772,7 @@ namespace SixLabors.ImageSharp.Tests
 
             public const string GrayscaleDeflateMultistrip = "Tiff/grayscale_deflate_multistrip.tiff";
             public const string GrayscaleUncompressed = "Tiff/grayscale_uncompressed.tiff";
+            public const string GrayscaleJpegCompressed = "Tiff/JpegCompressedGray.tiff";
             public const string PaletteDeflateMultistrip = "Tiff/palette_grayscale_deflate_multistrip.tiff";
             public const string PaletteUncompressed = "Tiff/palette_uncompressed.tiff";
             public const string RgbDeflate = "Tiff/rgb_deflate.tiff";

tests/Images/Input/Tiff/JpegCompressedGray.tiff

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:868afd018d025ed7636f1155c1b1f64ba8a36153b56c7598e8dee18ce770cd5a
+size 539660