Update listmonk icon.

listmonk/manifest.yaml

@@ -3,7 +3,7 @@ is: listmonk
 description: Listmonk is a standalone, self-hosted, newsletter and mailing list manager.
   It is fast, feature-rich, and packed into a single binary.
 version: 5.0.3
-icon: https://listmonk.app/static/images/logo.svg
+icon: https://cdn.jsdelivr.net/gh/homarr-labs/dashboard-icons/svg/listmonk.svg
 requires:
 - name: postgres
 defaultConfig: