What you are probably running into is that you are using ament_target_dependencies for a target that matches your project_name (from ${PROJECT_NAME}). However, you do not build a library or add an executable to assign those dependencies to. Later, you also try to install a target with the same${PROJECT_NAME}, and since there is no target CMake will most likely complain about that.
If you are not building any code, I would not install anything. However, you can still set dependencies for your package, just use the ament_export_dependencies call instead.