Add "id" to the fake system entity

* previously, this property was missing from the fake entity which would
  trip up notification builders

CHANGES.rst

@@ -12,6 +12,7 @@ Changes
 Version <next>
 
 - Allow secondary email address to be removed again
+- Add "id" to the fake entity created by `SystemEntityProxy._resolve()`
 
 
 Version 2025.1.8 (released 2025-02-13)

invenio_config_tuw/notifications/entity_resolvers.py

@@ -27,7 +27,11 @@ class SystemEntityProxy(EntityProxy):
         Since this will mostly be used in Jinja templates, it being a dictionary
         and not an actual object is fine.
         """
-        return {"username": "system", "user_profile": {"full_name": "System"}}
+        return {
+            "id": "system",
+            "username": "system",
+            "user_profile": {"full_name": "System"},
+        }
 
     def pick_resolved_fields(self, identity, resolved_dict):
         """Select which fields to return when resolving the reference."""