fix: Manage preference

templates/apt.conf.j2

@@ -1,6 +1,5 @@
 # {{ ansible_managed }}
 
-APT::Default-Release "stable";
 APT::Install-Recommends "false";
 APT::Install-Suggests "false";
 APT::Get::Show-Versions "true";

templates/preferences.j2

@@ -1,5 +1,9 @@
 # {{ ansible_managed }}
 
-Package: {{ item.package }}
-Pin: {{ item.pin }}
-Pin-Priority: {{ item.priority }}
+Package: *
+Pin: release a=testing
+Pin-Priority: -10
+
+Package: *
+Pin: release a=unstable
+Pin-Priority: -20