Update SDL group to use the ones defined and maintained by Arcade

#4

Matt's comment:

core-setup-sdl-validation exists and will allow your pipeline to run, but if this repo does Arcade onboarding you should consider having a "TODO"-type issue about using Arcade's SDL validation stuff so you aren't at the mercy of Davis' secrets expiring. (A shared place for secrets to expire makes it more likely to fix itself when things expire / cycle)