tests/avocado: add machine:none tag to version.py

This test currently fails when run on a host for which the QEMU target
has no default machine set:

ERROR| Output: qemu-system-aarch64: No machine specified, and there is
no default

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

tests/avocado/version.py

@@ -15,6 +15,7 @@ from avocado_qemu import QemuSystemTest
 class Version(QemuSystemTest):
     """
     :avocado: tags=quick
+    :avocado: tags=machine:none
     """
     def test_qmp_human_info_version(self):
         self.vm.add_args('-nodefaults')