Rollup merge of #145901 - stoeckmann:raw_vec_typo, r=samueltardieu

Fix typo in comment of library/alloc/src/raw_vec/mod.rs

Turn "any heap allocators" into "any heap allocator".

Shoutout to [Let's Read OSS](https://github.com/stoeckmann/lets-read-oss).

Author: samueltardieu