Bug#1006333: biboumi: fail to start after libexpat1 update

[Diane Trout]

FWIW I saw a more complex patch for this issue posted here

https://lab.louiz.org/louiz/biboumi/-/commit/0061298dd0945f7f67e7fa340c6649b179c804d5

from the Biboumi XMPP muc.

I added the patch to 9.0-4 and compiled it for bullseye, and it seems
to work.

I tried connecting to oftc.net and tried using the ad-hoc commands to
try to configure some irc settings.