Cher always appears to be glowing, but her Met Gala skin was something different. As it turns out, her makeup artist used a cult-favorite serum to give her that smooth, dewy appearance. Shoppers have labeled the find as “magical,” calling it “liquid youth” and an “instant glow in a bottle” — and somehow, it’s only $30! Cher’s pre-glam prep started with Charlotte Tilbury’s Magic Serum Crystal Elixir, a formula beauty editors have been quietly hoa…