erp5_oauth2_authorisation: use HTTPResponse.listHeaders() instead of accessing properties directly.

bt5/erp5_oauth2_authorisation/TestTemplateItem/portal_components/test.erp5.testOAuth2Server.py

@@ -409,13 +409,9 @@ class TestOAuth2(ERP5TypeTestCase):
       exc = None
     finally:
       setSecurityManager(current_security_manager)
-      cookie_dict = response.cookies.copy()
+      cookie_dict = {}
       response_header_dict = {}
-      for item_list in (
-        six.iteritems(response.headers),
-        response.accumulated_headers,
-      ):
-        for key, value in item_list:
+      for key, value in response.listHeaders():
         key = key.lower()
         if key == 'set-cookie':
           # XXX: minimal Set-Cookie parser