Fix isfinite implementation to be constexpr

The implementation failed to be constexpr in the situation where:
  __cplusplus == 202002L && !defined(__cpp_lib_is_constant_evaluated)

Fix fmtlib#3745

include/fmt/format.h

@@ -2752,7 +2752,7 @@ template <typename T, FMT_ENABLE_IF(std::is_floating_point<T>::value&&
                                         has_isfinite<T>::value)>
 FMT_CONSTEXPR20 bool isfinite(T value) {
   constexpr T inf = T(std::numeric_limits<double>::infinity());
-  if (is_constant_evaluated())
+  if (is_constant_evaluated(true))
     return !detail::isnan(value) && value < inf && value > -inf;
   return std::isfinite(value);
 }