chore: add string value for warning

    <string name="account_create_new_calendar">Create new calendar</string>

    <string name="account_no_webcal_handler_found">No Webcal-capable app found</string>

    <string name="account_install_icsx5">Install ICSx⁵</string>

    <string name="account_notification_invalid_login">Your login/password is incorrect, please login again.</string>

    <!-- AddAccountActivity -->

    <string name="login_title">Add account</string>

    <string name="login_eelo_title">Use your Murena ID to sign in (for example @e.email or @murena.io):</string>