[Bug]: Give the external storage warning the same style as other warnings displayed at the top of the settings dialog

### ⚠️ Before submitting, please verify the following: ⚠️

- [X] This is a **bug**, not a question or a configuration issue.
- [X] This issue is **not** already reported on Github (I've searched it).
- [X] Nextcloud Server and Desktop Client are **up to date**. See [Server Maintenance and Release Schedule](https://github.com/nextcloud/server/wiki/Maintenance-and-Release-Schedule) and [Desktop Releases](https://nextcloud.com/install/#install-clients) for supported versions.
- [X] I agree to follow Nextcloud's [Code of Conduct](https://nextcloud.com/contribute/code-of-conduct/)

### Bug description

The messages in the dialog have different styles:

### Steps to reproduce

1. Synchronize folders with external storages

### Expected behavior

The client should display a message in the same style as the other warnings/errors in the UI

### Which files are affected by this bug

None

### Operating system

Linux

### Which version of the operating system you are running.

Archlinux

### Package

Appimage

### Nextcloud Server version

28

### Nextcloud Desktop Client version

3.11.0

### Is this bug present after an update or on a fresh install?

Updated to a major version (ex. 3.3.6 to 3.4.0)

### Are you using the Nextcloud Server Encryption module?

Encryption is Disabled

### Are you using an external user-backend?

- [ ] Default internal user-backend
- [X] LDAP/ Active Directory
- [ ] SSO - SAML
- [ ] Other

### Nextcloud Server logs

_No response_

### Additional info

_No response_