There's a couple of sub Reddits/appliance forums out there with this very question, mystery pin found near or in their washing machine. They were similar in size/shape to yours. Apparently "it's a shipping pin used to prevent the tub and support from shifting during shipping. They are disengaged from their positions during installation via a cord or strap that you pull on to release them. There should be some little plastic cups that they fall into when released."