They might've been acting, but stars like Margot Robbie, Jenna Oretga and Cillian Murphy were not faking their talents on setFrom left: Margot Robbie as Tonya Harding in 2017's 'I, Tonya'; Jenna Ortega as Wednesday Addams on 'Wednesday' in 2022; Cillian Murphy as J. Robert Oppenheimer in 2023's 'Oppenheimer'Credit: 30West/Courtesy Everett Collection; Vlad Cioplea/Netflix; Universal PicturesSome actors don't just act the part — they become the pa…