Use forwarding references in UDL template

include/fmt/format.h

@@ -3455,13 +3455,13 @@ namespace internal {
 template <typename Char, Char... CHARS> class udl_formatter {
  public:
   template <typename... Args>
-  std::basic_string<Char> operator()(const Args&... args) const {
+  std::basic_string<Char> operator()(Args&&... args) const {
     FMT_CONSTEXPR_DECL Char s[] = {CHARS..., '\0'};
     FMT_CONSTEXPR_DECL bool invalid_format =
         do_check_format_string<Char, error_handler, Args...>(
             basic_string_view<Char>(s, sizeof...(CHARS)));
     (void)invalid_format;
-    return format(s, args...);
+    return format(s, std::forward<Args>(args)...);
   }
 };
 #  else