mailman2_download: fix list name check
According to the documentation here: https://hyperkitty.readthedocs.io/en/latest/install.html#importing-the-current-archives « LIST_NAME is the name of the mailing-list without the domain (before the @ sign) » And the Mailman 2.1 URLs use the short name indeed, as there was a single namespace.
Edited by username-removed-454952