C#: Add enum long type testcase.

Author: michaelnebel

csharp/ql/test/query-tests/Stubs/All/Test.cs

@@ -162,6 +162,12 @@ public enum Enum4
         None4 = 2,
         Some42 = 6
     }
+
+    public enum EnumLong : long
+    {
+        Some = 223372036854775807,
+        None = 10
+    }
 }
 
 namespace A1