fix header for apply_scalar_unary

SteveBronder · SteveBronder · commit 9fa2d3f68cce · 2025-08-15T11:34:20.000-04:00
diff --git a/stan/math/prim/functor/apply_scalar_unary.hpp b/stan/math/prim/functor/apply_scalar_unary.hpp
@@ -4,6 +4,7 @@
 #include <stan/math/prim/fun/Eigen.hpp>
 #include <stan/math/prim/meta/is_eigen.hpp>
 #include <stan/math/prim/meta/is_complex.hpp>
+#include <stan/math/prim/meta/holder.hpp>
 #include <stan/math/prim/meta/require_generics.hpp>
 #include <stan/math/prim/meta/is_vector.hpp>
 #include <stan/math/prim/meta/is_vector_like.hpp>
