Switch --destdir as --downloaddir was dropped in DNF5

[mildas]

https://dnf5.readthedocs.io/en/latest/changes.html

--downloaddir Dropped. Now only the --destdir is used for the download command.

Fedora Rawhide already switched to dnf5 - https://fedoraproject.org/wiki/Releases/41/ChangeSet#Switch_to_dnf5