Defence in depth is not just 'throw anything in that might improve security' though. The idea is to have multiple strong layers, not a hundred half-measures that are all easily bypassed. A stronger layer might be sandboxing, or separating your build and publishing steps as others have suggested (and also probably worth restricting the credentials the publishing step to just the relevant packages as well). These will at least robustly prevent a malicious dependency from spreading horizontally, but you'll still potentially ship malware to your customers.