docs(tree): ListItem doesn't have on_secondary_mouse_down

[zanmato]

ListItem doesn't have on_secondary_mouse_down, docs: https://github.com/longbridge/gpui-component/blob/main/docs/docs/components/tree.md?plain=1#L154-L166

Should it be added to ListItem?

.when_some(self.on_secondary_mouse_down, |this, on_mouse_down| {
    this.on_mouse_down(MouseButton::Right, move |event, window, cx| {
        (on_mouse_down)(event, window, cx)
    })
})