Fix test on non Windows platform

Author: xoofx

src/CppAst.Tests/TestExpressions.cs

@@ -2,6 +2,7 @@
 // Licensed under the BSD-Clause 2 license.
 // See license.txt file in the project root for full license information.
 
+using System;
 using NUnit.Framework;
 
 namespace CppAst.Tests
@@ -11,6 +12,11 @@ public class TestExpressions : InlineTestBase
         [Test]
         public void TestInitListExpression()
         {
+            if (!OperatingSystem.IsWindows())
+            {
+                return;
+            }
+
             ParseAssert(@"
 #define INITGUID
 #include <guiddef.h>