Only show ellipsis if the button's interactable (#6373)

* Add an indicator to make the undo renote button look more interactable

* Use faEllipsisH :art

* Only show elipsis if it's interactable

* Update note.vue

Co-authored-by: DW <chocological00@gitlab.com>
Co-authored-by: syuilo <Syuilotan@yahoo.co.jp>