tests/functional/test_s390x_tuxrun: Check whether the machine is available The s390x tuxrun test lacks the call to self.set_machine(), so this test is currently failing in case the 's390-ccw-virtio' machine has not been compiled into the binary. Add the check now to fix it. Signed-off-by: Thomas Huth <thuth@redhat.com> Message-ID: <20250424090640.664217-1-thuth@redhat.com>