[fix] Use the classic way to create read-only bind mount in ynh_backup
[fix] Use the classic way to create read-only bind mount in ynh_backup

YunoHost/yunohost,YunoHost/moulinette-yunohost,YunoHost/moulinette-yunohost,YunoHost/yunohost,YunoHost/moulinette-yunohost,YunoHost/moulinette-yunohost,YunoHost/moulinette-yunohost,YunoHost/yunohost,YunoHost/yunohost