Art Gallery of Ontario is set to welcome back visitors this month with a much-hyped exhibition of the pop-art phenom Andy Warhol.The Toronto gallery says it’s preparing to reopen on July 21, pending final confirmation from provincial and local authorities.Art lovers can purchase tickets to see more than 250 of Warhol’s works, including such iconic images as “Campbell’s Soup Cans” and “Marilyn Diptych.”AGO members will be first in line for access to the exhibition between July 21 and 25.