fix: ensure timeout not nil to avoid `attempt to perform arithmetic o…

…n a nil value` error

lib/resty/etcd/v3.lua

@@ -507,6 +507,7 @@ function refresh_jwt_token(self, timeout)
     end
 
     if self.requesting_token then
+        timeout = timeout or self.timeout or 0
         self.sema:wait(timeout)
         if self.jwt_token and now() - self.last_auth_time < 60 * 3 + random(0, 60) then
             return true, nil