add FIXME: where it belongs

suggestion from a friend!! 🐸

Co-authored-by: Michael Goulet <michael@errs.io>

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -64,7 +64,7 @@ impl<'a> Comments<'a> {
  Comments { sm, comments, current: 0 }
  }
 
- // This shouldn't probably clone lmao
+ // FIXME: This shouldn't probably clone lmao
  pub fn next(&self) -> Option<Comment> {
  self.comments.get(self.current).cloned()
  }