Callout box with type `info` changes color with theme

[mejo-]

Describe the bug
The border color of callout boxes with type info currently is set to var(--color-primary-element). This variable can be changed in custom themes.

Instead, we should probably hardcode it to #006aa3 for now and use var(--color-info) once it got introduced.

See nextcloud-libraries/nextcloud-vue#4063 (comment).

[mejo-]

nextcloud/server#38205 introduces var(--color-info). Once it got merged, we could switch to it but should still set #006aa3 as fallback for backwards-compatibility.

[max-nextcloud]

I'd be tempted to just migrate to using Nextcloud vues note card and not backport this.

But maybe that's two steps indeed. A fix with a hard coded default that can be backported and then the migration.

[max-nextcloud]

We are using Nextcloud vue 7 since stable25. So maybe we could move to using the component right away to fix this and backport all the way to stable25 with minor version bumps of Nextcloud vue.

update: the addition in Nextcloud vue still requires Nextcloud 27. So that is not an option.