[netinstall] Massage test data

- hidden groups aren't counted at all
- count() at top-level of the model counts groups

src/modules/netinstall/tests/data-small.yaml

@@ -1,12 +1,17 @@
 # SPDX-FileCopyrightText: no
 # SPDX-License-Identifier: CC0-1.0
 #
----
 - name: "Default"
   description: "Default group"
-  hidden: true
+  hidden: false
   selected: true
   critical: false
   packages:
     - base
+- name: "Second"
+  description: "Second group"
+  hidden: false
+  selected: true
+  critical: false
+  packages:
     - chakra-live-skel