erp5_credential: fix Python3Style test

i noticed we have one python3style test failed with

@@ -164,7 +164,7 @@
       self.portal.portal_workflow._jumpToStateFor(assignment_request,
           'submitted')
       assignment_request.AssignmentRequest_changeAssignment()
-      self.assertEquals(assignment_request.getSimulationState(), 'validated')
+      self.assertEqual(assignment_request.getSimulationState(), 'validated')

       self.tic()
       self.assertAlarmNotVisitingDocument(