macOS: Fix build error due to std::optional<T>::value

Added in rBc5514d3a2a03242ddc43f83be4bb72df7f85469f

source/blender/modifiers/intern/MOD_nodes.cc

@@ -280,7 +280,7 @@ class GeometryNodesEvaluator {
             &socket_to_compute, from_socket);
         std::optional<GMutablePointer> value = value_by_input_.pop_try(key);
         if (value.has_value()) {
-          values.append(value.value());
+          values.append(*value);
         }
         else {
           this->compute_output_and_forward(*from_socket);