Add snapshots for sub menus in nano devices

[dfordivam]

Currently the tests don't take snapshots of the sub menus inside "settings" and "about".
It would be better if the contents of these are also tested.

https://github.com/LedgerHQ/app-boilerplate-rust/blob/main/tests/snapshots/nanosp/test_app_mainmenu/00001.png