Disable unserialized arguments check for py2

Author: aadamson

testing/acceptance_test.py

@@ -1,5 +1,6 @@
 import os
 import re
+import sys
 import textwrap
 
 import py
@@ -808,6 +809,9 @@ def test_unserializable_warning_details(self, testdir, n):
         """Check that warnings with unserializable _WARNING_DETAILS are
         handled correctly (#379).
         """
+        if sys.version_info[0] < 3:
+            # The issue is only present in Python 3 warnings
+            return
         testdir.makepyfile(
             """
             import warnings, pytest