Cirrus-CI: use qemu-nox11

We use -nographic for the smoke test and there is no need to pull in all
of the x11 deps. This saves some time and bandwidth during package
installation.

When I originally added Cirrus-CI support the -nox11 package was not
available.

Sponsored by: The FreeBSD Foundation

(cherry picked from commit e510f97b4814f5ddb8169bf378030a31a99545d9)