fix(glm4v): bump backend_equivalence_atol to 0.5 for Pillow 13 compatibility (#50170)
Pillow >= 13 changed the order of bicubic resize passes (vertical-first when
height shrinks more than width), producing slightly different pixel values when
compared against torchvision. Matches the fix applied to other models in #50105.
Co-authored-by: ydshieh <ydshieh@users.noreply.github.com>