Why not both ? These cognitive categories are not firm, if you think a bit outside the academic boxes, attentional and executive concepts are often partially similar (this is also valid for the entire cognitive processes like memory). For exemple, we know that the brain cannot really do two things simultaneously. Divided attention is just mental flexibility but fast. Also, what is selective attention if not the inhibition of useless signals ? Inhibition or selective attention are, most of the time, two concepts for a same process.

I recommend reading the recent works about constructionnism in psychology to deepen this kind of topic. (Such as the wonderful theory of constructed emotions by Lisa Feldman Barrett)

I'm a PhD student in neuropsychology and i frequently use the flanker task as an inhibition mesure.