refetor: 修改get_ticket_sn 参数type

apps/wf/services.py

@@ -97,12 +97,10 @@ class WfService(object):
         return Transition.objects.filter(**kwargs).all()
 
     @classmethod
-    def get_ticket_sn(cls, workflow: Workflow, now: str = ''):
+    def get_ticket_sn(cls, workflow: Workflow, now=datetime.now()):
         """
         生成工单流水号
         """
-        if now == '':
-            now = datetime.now()
         today = str(now)[:10]+' 00:00:00'
         ticket_day_count_new = Ticket.objects.get_queryset(all=True).filter(
             create_time__gte=today, create_time__lte=now, workflow=workflow).count()