Exception safety statement regarding Box contradicted by std docs

[gfaster]

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 is called, which is documented as potentially panicking.