Not only is there no way to report spam on Google Drive, I noticed in the past few months that Google have also started refusing spam reports via SpamCop. Now those reports just go to google-abuse-bounces-reports@devnull[0].
I suppose relative to their market size one could make an argument that they are doing a good job of “only” being the source of ~1.8% of all spam[1], and who knows what they did with these reports to begin with, but the intentional deterioration of reporting capability isn’t a great look, and there’s no effective recourse since they are too big to block outright.