Don't use GetWReference (it should return span)

src/ImageSharp/Formats/Jxl/Processing/Modular/Encoding/ContextPrediction/JxlContextPrediction.cs

@@ -2,7 +2,6 @@
 // Licensed under the Six Labors Split License.
 
 using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
 
 namespace SixLabors.ImageSharp.Formats.Jxl.Processing.Modular.Encoding.ContextPrediction;
 
@@ -17,8 +16,7 @@ internal static class JxlContextPrediction
 
     public static void SetPredictorMode(int i, JxlModularHeader header)
     {
-        ref uint wr = ref header.GetWReference();
-        Span<uint> w = MemoryMarshal.CreateSpan(ref wr, 4);
+        Span<uint> w = header.GetW();
 
         switch (i)
         {

src/ImageSharp/Formats/Jxl/Processing/Modular/Encoding/ContextPrediction/JxlModularHeader.cs

@@ -101,10 +101,10 @@ internal sealed class JxlModularHeader : IJxlFields
     }
 
     /// <summary>
-    /// Returns a reference to the first w item.
+    /// Returns a span to the w array.
     /// </summary>
-    /// <returns>Reference to w[0]</returns>
-    public ref uint GetWReference() => ref this.w[0];
+    /// <returns>Reference to w</returns>
+    public Span<uint> GetW() => this.w;
 
     public bool Visit(JxlVisitor v)
     {

src/ImageSharp/Formats/Jxl/Processing/Modular/Encoding/ContextPrediction/JxlModularState.cs

@@ -109,13 +109,13 @@ internal sealed class JxlModularState
         int posNW = x > 0 ? posN - 1 : posN;
 
         Span<uint> weights = stackalloc uint[4];
-        ref uint headerW = ref this.header.GetWReference();
+        Span<uint> headerW = this.header.GetW();
 
         for (int i = 0; i < 4; i++)
         {
             Span<uint> error = this.predErrors[i].AsSpan();
             weights[i] = error[posN] + error[posNE] + error[posNW];
-            weights[i] = ErrorWeight((int)weights[i], Unsafe.Add(ref headerW, i));
+            weights[i] = ErrorWeight((int)weights[i], headerW[i]);
         }
 
         n = AddBits(n);