在商户后台配置了回调地址并发起退款，收到的回调验签时Wechatpay-Serial是空的

log: "msg":"[func]ParseRequest: ParseRequest getNotification fail, err: invalid notification, err: key `Wechatpay-Serial` is empty in header, request-id=[]

Header:map[Accept:[*/*] Cache-Control:[no-cache] Content-Length:[1405] Content-Type:[text/xml] Pragma:[no-cache] User-Agent:[Mozilla/4.0] X-B3-Parentspanid:[c3aff444071f64d7] X-B3-Sampled:[0] X-B3-Spanid:[bda356e521ccedfb] X-B3-Traceid:[7ae3893a3f5fe98fc3aff444071f64d7] X-Envoy-Attempt-Count:[1] X-Envoy-External-Address:[175.24.211.24] X-Forwarded-For:[175.24.211.24] X-Forwarded-Proto:[https] X-Request-Id:[dd6cd87b-18b6-4934-925e-ef1218faa473]]