There's a persistent problem with installing `gnome-icon-theme' on
emulated ARM platforms, resulting in
Unpacking gnome-icon-theme (3.12.0-2) ...
dpkg: error processing archive /tmp/apt-dpkg-install-AtXukB/100-gnome-icon-theme_3.12.0-2_all.deb (--unpack):
corrupted filesystem tarfile - corrupted package archive
Upgrading to buster's Qemu let to a successful build once, so maybe this
helps.