fail2ban currently installs its fail2ban.service file into
/usr/lib/systemd/system/, but dh_installsystemd does not
handle files in this location (#1031695).

It seems like fail2ban moved the file in this commit:
https://salsa.debian.org/python-team/packages/fail2ban/-/commit/bdb82eb3b26485f9ec585896503d3afeed812dc1

If fail2ban wants the automatic install/start/restart
behaviour, and I think it does, because that works in bullseye, probably
that commit needs a revert for bookworm.

Chris