fix(validation): align btrfs disk size check with new 2GB swap minimum

roles/global_defaults/tasks/validation.yml

@@ -259,7 +259,7 @@
               (system_cfg.memory | float / 1024 >= 16.0)
               | ternary(
                   (system_cfg.memory | float / 2048),
-                  [system_cfg.memory | float / 1024, 4.0] | max
+                  [system_cfg.memory | float / 1024, 2.0] | max
                 )
             )
             + 5.5