Take the span type from the array conversion's return type

MatchArrayInitializerFinal selects the operator by its return type, so
the block's result type is that return type. The declaring type only
happens to be the same one for the two array-to-span operators; Span<T>
also declares the conversion to ReadOnlySpan<T>.

Assisted-by: Claude:claude-opus-5:Claude Code

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -3966,8 +3966,8 @@ namespace ICSharpCode.Decompiler.CSharp
 			var initializer = expr.WithILInstruction(block).WithRR(rr);
 			if (arrayToSpan != null)
 			{
-				var arrayToSpanRR = new ConversionResolveResult(arrayToSpan.DeclaringType, rr, Conversion.ImplicitSpanConversion);
-				initializer = new CastExpression(ConvertType(arrayToSpan.DeclaringType), expr).WithoutILInstruction().WithRR(arrayToSpanRR);
+				var arrayToSpanRR = new ConversionResolveResult(arrayToSpan.ReturnType, rr, Conversion.ImplicitSpanConversion);
+				initializer = new CastExpression(ConvertType(arrayToSpan.ReturnType), expr).WithoutILInstruction().WithRR(arrayToSpanRR);
 			}
 			return initializer;
 		}