Bug#1061788: bookletimposer fails its autopkg tests with Python 3.12

[Graham Inggs]

Control: reopen -1

Still failing with bookletimposer/0.3.1-4 [1].  Please see one of the logs
triggered by python3-defaults/3.12.1-1 from experimental.


[1] https://ci.debian.net/packages/b/bookletimposer/unstable/amd64/