playbook_sysupgrade: stringify garet_release

when garet_release only contains digets, playbook_sysupgrade compared
the string from the device itself against an integer from the inventory
always triggering an upgrade.

This should fix this corner case

playbook_sysupgrade.yml

@@ -16,6 +16,10 @@
       setup:
         filter: ansible_local
 
+    - name: stringify garet_release...
+      set_fact:
+        garet_release: "{{ garet_release | string }}"
+
     - name: handle update
       block:
         - name: upload new firmware