CacheDir on an NFS share no longer works since Pacman 7

Related BBS thread: https://bbs.archlinux.org/viewtopic.php?id=299473

Since Pacman 7, configuring CacheDir to a directory on an NFS share will result in no ability to download packages:

:: Proceed with download? [Y/n] 
debug: using cachedir: /n/pacman/cache/
error: failed to commit transaction (unexpected error)
Errors occurred, no packages were upgraded.

Unsetting the DownloadUser option allows the package to be downloaded, but the transaction still fails:

:: Retrieving packages...
 ddcutil-2.1.4-2-x86_64 downloading...
...
debug: curl_download_internal return code is 0
warning: failed to retrieve some files
error: failed to commit transaction (unexpected error)

This happens because of two new chown calls performed as root, which don't play nicely with NFS' root_squash/all_squash options (where root_squash is the NFS default):

• libalpm/util.c – _alpm_temporary_download_dir_setup() – changes the ownership of temporary download directory to the user set in DownloadUser;
• libalpm/dload.c – finalize_download_file() – changes the ownership of downloaded files to root.

NFS squashing makes changing ownership an invalid operation, even though target user can still have read/write permissions to a file/directory in question.

Modifying the code so that the return values of these chown calls are ignored makes Pacman successfully download packages.

There doesn't seem to be a way to fix this on NFS share's side other than by setting no_root_squash, which might not be desirable.