ASN Lookup expert database update fails after the 28th of each month

intelmq@localhost:~$ intelmq.bots.experts.asn_lookup.expert --update-database
Searching for the latest database update...
Database update failed. Couldn't find the latest database update.

haven't yet investigated the reasons

As @schacht-certat found out, the issue was that the server had an empty directory named "2021.09" yesterday. Today it works fine again. Should be handled though.

That fails at the end of every month. The monthly directories in http://archive.routeviews.org/route-views4/bgpdata/ are always created on the 28th of the previous month and thus our code fails on every 29th, 30th and 31st of each month.