fix template requires for bessel_second_kind

Author: SteveBronder

stan/math/prim/fun/bessel_second_kind.hpp

@@ -53,7 +53,7 @@ inline T2 bessel_second_kind(int v, const T2 z) {
  * @return Bessel second kind function applied to the two inputs.
  */
 template <typename T1, typename T2, require_any_container_t<T1, T2>* = nullptr,
-          require_not_var_matrix_t<T2>* = nullptr>
+          require_not_var_t<T2>* = nullptr>
 inline auto bessel_second_kind(T1&& a, T2&& b) {
   return apply_scalar_binary(
       [](auto&& c, auto&& d) {