internal -> detail (#1538)

test/std-format-test.cc

@@ -124,7 +124,7 @@ template <> struct std::formatter<S> {
           if constexpr (!is_integral_v<type> || is_same_v<type, bool>)
             throw format_error("width is not integral");
           // else if (value < 0 || value > numeric_limits<int>::max())
-          else if (fmt::internal::is_negative(value) ||
+          else if (fmt::detail::is_negative(value) ||
                    value > numeric_limits<int>::max())
             throw format_error("invalid width");
           else