You could be direct with the coworker and call them out on their ulterior motive to pad their resume, but if you've misjudged their motive you'll look silly. If being direct is not an option, attempts to dissuade the coworker from using shiny tech overall won't work. Two suggestions --

* A more granular pushback is needed, for instance, "we shouldn't be using package X because it's not MIT license" or "the package has a higher memory footprint for what we need, have you tried package Y instead."Document these pushback arguments into a checklist to ensure your coworker has checked off before using new shiny tech.

* Convince others rather than your coworker of arguments against using shiny packages, articulated in terms of delay, extra cost, problems down the road, etc. It's an indirect approach but you won't be alone in pushing back on the coworker's scheme.