Disable DynamicCode_Jit test from System.Runtime.Tests on Mono (#228)

It fails on mono with interpreter (IsDynamicCodeCompiled is false).

Author: EgorBo

src/libraries/System.Runtime/tests/System/Runtime/CompilerServices/RuntimeFeatureTests.cs

@@ -5,6 +5,7 @@
 using System;
 using System.Runtime.CompilerServices;
 using Xunit;
+using Microsoft.DotNet.XUnitExtensions.Attributes;
 
 namespace System.Runtime.CompilerServices.Tests
 {
@@ -29,6 +30,7 @@ public static void DynamicCode()
         }
 
         [Fact]
+        [SkipOnMono]
         public static void DynamicCode_Jit()
         {
             Assert.True(RuntimeFeature.IsDynamicCodeSupported);