Disable some of the tests for mono

• Haven't opened an issue for this yet - will follow up with an issue & commit to add the issue link

src/libraries/System.Runtime/tests/System/Type/TypeTests.cs

@@ -1212,7 +1212,8 @@ public static IEnumerable<object[]> GetInterfaceMap_TestData()
                 }
 
                 // Check we have the expected implementation for the level 3 interfaces (abstract explicit implementations - I1.M and I1.G methods)
-                if (classType.Index >= 3)
+                bool isMono = typeof(object).Assembly.GetType("Mono.RuntimeStructs") != null; // [ActiveIssue("https://github.com/dotnet/runtime/issues/TODO")]
+                if (!isMono && classType.Index >= 3)
                 {
                     foreach ((Type Type, string MethodNamePrefix) interfaceType in new (Type, string)[]
                         {