Unpin a post from its channel
unpin_post.RdRemove a post's pinned status from the channel. This is the semantic endpoint for unpinning; the same effect can be achieved via `update_post(post_id, is_pinned = FALSE)`.
unpin_post.RdRemove a post's pinned status from the channel. This is the semantic endpoint for unpinning; the same effect can be achieved via `update_post(post_id, is_pinned = FALSE)`.