Fix file header copyright text

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

@@ -1,5 +1,5 @@
 // Copyright (c) Six Labors.
-// Licensed under the Apache License, Version 2.0.
+// Licensed under the Six Labors Split License.
 
 using System;
 using System.Buffers;

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

@@ -1,5 +1,5 @@
 // Copyright (c) Six Labors.
-// Licensed under the Apache License, Version 2.0.
+// Licensed under the Six Labors Split License.
 
 using System;
 using System.Numerics;