I can't find anything solid, but old posts of it seem to consistently say it's just a promo photo. They are wearing these costumes for a brief shot upon them first riding back into the Shire

The film (including the extended edition) cuts the Scouring altogether. I personally think it was the right choice for the film, which already feels a bit like it ends several times. Great addition to the book for how it shows the change the journey has made on the characters, but a sensible change when adapting to another medium in my opinion