caddyhttp: Log 4xx as INFO; 5xx as ERROR (close #6106)

modules/caddyhttp/server.go

@@ -784,7 +784,7 @@ func (s *Server) logRequest(
 	// wrapping may return multiple loggers, so we log to all of them
 	for _, logger := range loggers {
 		logAtLevel := logger.Info
-		if wrec.Status() >= 400 {
+		if wrec.Status() >= 500 {
 			logAtLevel = logger.Error
 		}
 		message := "handled request"