test: Update benchmark code to compile with C#14

C#14 has a breaking change. It prefers to use ReadOnlySpan when doing an implicit conversion from an array.
Use an explicit method as we a conversion to a normal Span.

Author: vbaderks

benchmark/Micro/GenericColorTransformation.cs

@@ -109,7 +109,7 @@ public void Init()
     public void TransformHP1Explicit()
     {
         var sourceTriplet = MemoryMarshal.Cast<byte, Triplet<byte>>(_source);
-        var destinationTriplet = MemoryMarshal.Cast<byte, Triplet<byte>>(_destination);
+        var destinationTriplet = MemoryMarshal.Cast<byte, Triplet<byte>>(_destination.AsSpan());
 
         for (int i = 0; i < PixelCount; ++i)
         {
@@ -122,7 +122,7 @@ public void TransformHP1Explicit()
     public void TransformHP1ExplicitIntParameters()
     {
         var sourceTriplet = MemoryMarshal.Cast<byte, Triplet<byte>>(_source);
-        var destinationTriplet = MemoryMarshal.Cast<byte, Triplet<byte>>(_destination);
+        var destinationTriplet = MemoryMarshal.Cast<byte, Triplet<byte>>(_destination.AsSpan());
 
         for (int i = 0; i < PixelCount; ++i)
         {
@@ -135,7 +135,7 @@ public void TransformHP1ExplicitIntParameters()
     public void TransformHP1ExplicitIntParametersReturnTripletByte()
     {
         var sourceTriplet = MemoryMarshal.Cast<byte, TripletByte>(_source);
-        var destinationTriplet = MemoryMarshal.Cast<byte, TripletByte>(_destination);
+        var destinationTriplet = MemoryMarshal.Cast<byte, TripletByte>(_destination.AsSpan());
 
         for (int i = 0; i < PixelCount; ++i)
         {
@@ -195,7 +195,7 @@ public void TransformHP1PerByte()
     public void TransformHP1Generic()
     {
         var sourceTriplet = MemoryMarshal.Cast<byte, Triplet<byte>>(_source);
-        var destinationTriplet = MemoryMarshal.Cast<byte, Triplet<byte>>(_destination);
+        var destinationTriplet = MemoryMarshal.Cast<byte, Triplet<byte>>(_destination.AsSpan());
 
         for (int i = 0; i < PixelCount; ++i)
         {