function 'kangaru::placeholder_source::provide<kangaru::source_reference_wrapper<kangaru::modular_source<kangaru::source_reference_wrapper<kangaru::modular_source<>>, (lambda at /home/runner/work/kangaru/kangaru/tests/src/5-playground.cpp:258:3), (lambda at /home/runner/work/kangaru/kangaru/tests/src/5-playground.cpp:262:3)>>>' has internal linkage but is not defined [-Wundefined-internal]