Disable CS0419 in test to avoid warnings after code fix is applied

I'm unabled to reproduce this issue in Visual Studio 2017, so it could be a
bug that only manifests in API usage of Roslyn or has since been fixed.

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers.Test/ReadabilityRules/SA1121UnitTests.cs

@@ -663,7 +663,8 @@ public class Foo
         [MemberData(nameof(AllTypes))]
         public async Task TestDocumentationCommentDirectReferenceCodeFixAsync(string predefined, string fullName)
         {
-            string testCode = @"namespace System {{
+            string testCode = @"#pragma warning disable CS0419 // Ambiguous reference in cref attribute
+namespace System {{
 /// <seealso cref=""{0}""/>
 public class Foo
 {{