Icon of notification is not an absolute URL and does not work in mobile and desktop clients

Steps to reproduce

1. Have Nextcloud 30.0.2 installed and files_antivirus app 5.6.1 installed
2. Observe loads of warning messages appear in Nextcloud logs similar to those posted here.

Expected behaviour

Warnings like these should not occur, there is a known fix for other apps that ran into this issue.

Actual behaviour

Tell us what happens instead, if possible also add a screenshot

Server configuration

I run Nextcloud AIO and it reports version 30.0.2

{"reqId":"Qj4mij9Rb9YkIZ5tzMAf","level":2,"time":"2024-12-07T10:54:34+00:00","remoteAddr":"<REDACTED_IP>","user":"<User Redacted>","app":"no app in context","method":"GET","url":"/ocs/v2.php/apps/notifications/api/v2/notifications","message":"Icon of notification is not an absolute URL and does not work in mobile and desktop clients [app: files_antivirus, subject: virus_detected_scan]","userAgent":"Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/131.0.0.0 Safari/537.36","version":"30.0.2.2","data":[],"id":"67542c027e2c4"}

Related issues and pull request that show a possible solution hint.
https://github.com/nextcloud/survey_client/pull/317
https://github.com/nextcloud/survey_client/issues/316

Start in the files_antivirus app by tracing the notification entry for the virus_detected_scan subject. Compare its icon handling with the proposed solution in survey_client pull request 317 and issue 316; done means the notification icon is an absolute URL and the warning no longer appears for mobile and desktop clients.