bookworm incompatible with python 3.13: Use removed module imghdr

[hosiet]

Downstream bug report: https://bugs.debian.org/1084657

As shown in

bookworm/data/scripts/mobi_lib/mobi_cover.py

Line 11 in 7bc7646

import imghdr

, bookworm is using the deprecated Python module imghdr, which has been removed in Python 3.13.0 release. Please update the source code to make it compatible with Python 3.13.

[babluboy]

Thanks for thid issue. I'm trying to upgrade bookworm to GTK 4 and will try and address this during the same. Keeping this issue open to remind me for imghdr update