Rollup merge of #140062 - xizheyin:issue-139958, r=workingjubilee

std: mention `remove_dir_all` can emit `DirectoryNotEmpty` when concurrently written into

Closes #139958

The current documentation for `std::fs::remove_dir_all` function does not explicitly mention the error types that may be returned in concurrent scenarios. Specifically, when one thread attempts to remove a directory tree while another thread simultaneously writes files to that directory, the function may return an `io::ErrorKind::DirectoryNotEmpty` error, but this behavior is not clearly mentioned in the current documentation.

r? libs

Author: GuillaumeGomez