[Conf] Align ARC scores with DKIM scores

conf/scores.d/policies_group.conf

@@ -126,13 +126,13 @@ symbols = {
     }
 
     "ARC_REJECT" {
-        weight = 2.0;
+        weight = 1.0;
         description = "ARC checks failed";
         groups = ["arc"];
     }
 
     "ARC_INVALID" {
-        weight = 1.0;
+        weight = 0.5;
         description = "ARC structure invalid";
         groups = ["arc"];
     }