[Fix] received: filtering of artificial header

rules/headers_checks.lua

@@ -42,7 +42,7 @@ local rcvd_cb_id = rspamd_config:register_symbol{
     local nreceived = fun.reduce(function(acc, rcvd)
         return acc + 1
       end, 0, fun.filter(function(h)
-        return not h['artificial']
+        return not h['flags']['artificial']
       end, received))
 
     for k,v in pairs(cnts) do

src/plugins/lua/once_received.lua

@@ -44,7 +44,7 @@ local function check_quantity_received (task)
   local nreceived = fun.reduce(function(acc, _)
     return acc + 1
   end, 0, fun.filter(function(h)
-    return not h['artificial']
+    return not h['flags']['artificial']
   end, recvh))
 
   local function recv_dns_cb(_, to_resolve, results, err)