It appears that James Gunn's The Suicide Squad has become the new Denis Villeneuve's Dune, which itself was the new Quentin Tarantino's Once Upon a Time in Hollywood, a.k.a. the massively stacked project that pops out a new casting announcement every day that ends with a Y. Today, Gunn pulled a new actor from the cosmos, as former Doctor Who star Peter Capaldi joins the project in an undisclosed role. Deadline also reports that Saturday Night Live breakout and alleged large-dong-haver Pete Davidson is in talks for a cameo role, that he'll …