Harvard’s striking cafeteria workers got another celebrity endorsement this week. Comedian Keegan-Michael Key, who’s in town shooting the Netflix series “Friends From College,” showed support for the workers by holding one of their signs. Unite Here Local 26, the union that represents the 750 dining hall workers, posted a pic of Key on Facebook. Last week, a photo of Ben Stiller surfaced on social media showing the “Something About Mary” star holding a “Support the Strike” sign while on a break from shooting a movie in Harvard Square. Local 26 wants an increase in the annual minimum pay from $30,000 to $35,000, and no increase in health care premiums.