Auto merge of #103406 - Jules-Bertholet:from_clone_slice_to_box, r=dtolnay

Loosen `From<&[T]> for Box<[T]>` bound to `T: Clone`

Also loosens `From<Cow<'_, [T]>> for Box<[T]>`'s bound.

[Discussion on Zulip](https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/From.3C.26.5BT.5D.3E.20impls.20consistency)

Author: bors