Add specific explicit interfaces to not have to modify the test.

LibGit2Sharp.Tests/MetaFixture.cs

@@ -17,7 +17,7 @@ public class MetaFixture
     {
         private static readonly HashSet<Type> explicitOnlyInterfaces = new HashSet<Type>
         {
-            typeof(IBelongToARepository), typeof(IDiffResult<>),
+            typeof(IBelongToARepository), typeof(IDiffResult<Patch>), typeof(IDiffResult<TreeChanges>), typeof(IDiffResult<PatchStats>),
         };
 
         [Fact]