Exception safety statement regarding Box contradicted by std docs

https://github.com/rust-lang/nomicon/blob/91044a66c8342ce3a85ebf5bc3f6811a39843990/src/unchecked-uninit.md?plain=1#L32

This asserts that `Box::new` cannot panic, but of course, it may fail to allocate in which case [`handle_alloc_error`](https://doc.rust-lang.org/std/alloc/fn.handle_alloc_error.html) is called, which is documented as potentially panicking.