test: Add unit tests for circuit_send_next_onion_skin()
This is a core function that has just been refactored with #22804 (moved) and is modified by #22810 (moved).
Whatever happens, we need unit tests for this as we have none now.
This is a core function that has just been refactored with #22804 (moved) and is modified by #22810 (moved).
Whatever happens, we need unit tests for this as we have none now.