The "Spirit Object" hex doesn't have the attack trait.
That might be intentional - treating the target object as if it were an animated or summoned minion for one round.
Or it may have been left off in order to avoid confusion if one casts the one-action version that doesn't attack, with the assumption being that the two-action version was "obviously" an attack spell.
Or it might have been an oversight, since in the two-action version the attack roll is made using the caster's "spell attack roll."
The answer to this question will held determine whether or not Baba Yaga witches should even bother considering carrying a sling.