community/gnome-boxes: fix creating machines by disabling smartcard support

Fixes #12998 (closed).

Technically, the correct way to fix this would be to enable smartcard support in QEMU, however this would require packaging libcacard, and since spice (which is in main) would have to be rebuilt it would also require libcacard and its dependencies (nss and opensc, which are in community) to be moved to main, or for spice and the one package in main that depends on it to be moved to community. See !25160 (closed) for a packaging attempt.