By Bonnie Stiernberg By all accounts, pop-punk is enjoying a full-blown resurgence these days. Contemporary artists like Machine Gun Kelly, Willow Smith and even Olivia Rodrigo have embraced the genre on recent releases, and early-’00s mainstays like Avril Lavigne are currently pushing new albums. This October, LiveNation’s new, aptly named When We Were Young festival will give the Warped Tour a run for its money with a lineup dominated by pop-punk and emo staples from two decades ago. On the one hand, it feels natural: pop culture is cyclical, and sooner or later these sounds and styles were …