Rollup merge of #126561 - kadiwa4:boxed_slice_into_iter_doc, r=jieyouxu

`boxed_slice_into_iter`: tiny doc correction

`CURRENT_RUSTC_VERSION` isn't flexible enough for this, so it got replaced by 1.80.0 instead of 1.79.0 in #126273 :/

Author: jieyouxu