Make color converter static

Co-authored-by: Günther Foidl <gue@korporal.at>

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/CieLabPlanarTiffColor{TPixel}.cs

@@ -17,7 +17,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
     internal class CieLabPlanarTiffColor<TPixel> : TiffBasePlanarColorDecoder<TPixel>
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        private readonly ColorSpaceConverter colorSpaceConverter = new();
+        private static readonly ColorSpaceConverter colorSpaceConverter = new();
 
         private const float Inv255 = 1.0f / 255.0f;
 

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/CieLabTiffColor{TPixel}.cs

@@ -16,7 +16,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
     internal class CieLabTiffColor<TPixel> : TiffBaseColorDecoder<TPixel>
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        private readonly ColorSpaceConverter colorSpaceConverter = new();
+        private static readonly ColorSpaceConverter colorSpaceConverter = new();
 
         private const float Inv255 = 1.0f / 255.0f;