Currently, the debian-gnome team is working on upgrading some core GNOME dependencies from 3.22 to 3.24/3.25 [1].
As a part of this effort, the gnome-tweak-tool was upgraded from 3.22.0-1 to 3.25.91-1. However, it appears that gnome-tweak-tool 3.25.91-1 is broken as it depends on gnome-shell >= 3.24.
According to the bug report [2], debian sid will soon get the gnome-shell 3.24, so this issue should be fixed soon.
[1] https://www.0d.be/debian/debian-gnome-3.24-status.html
[2] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=873765