[Py] fix function_wrapper_t struct tag

Author: tttapa

interfaces/python/src/problem/problems.py.cpp

@@ -32,7 +32,7 @@ using namespace py::literals;
 #if ALPAQA_WITH_DL
 template class ALPAQA_PYTHON_EXPORT std::span<std::string_view>;
 template class ALPAQA_PYTHON_EXPORT std::tuple<py::args, py::kwargs>;
-template class ALPAQA_PYTHON_EXPORT
+template struct ALPAQA_PYTHON_EXPORT
     alpaqa::detail::function_wrapper_t<py::object(void *, py::args, py::kwargs)>;
 #endif