Build new debian stable/unstable (qt 6.4)

python2 is removed from those distributions but webengine in 6.2.4 stills needs it.

Building 6.4.2 causes crashes whenever in a video. So we can't use 6.4.x right now.

Solution:

• wait for 6.2.5
• Wait for 6.4.x or 6.5

Provide minimal reproducible code for https://bugreports.qt.io/browse/QTBUG-110443

Ongoing patch: https://review.jami.net/c/jami-client-qt/+/23698