test: extend exact-shape assertion in relay-delivery guard for provenance tag

tests/cron/test_cron_relay_delivery_guards.py landed on main after #89329
branched; its exact-dict assertion needs the new _resolved_from field the
salvaged commit adds to origin-resolved targets.

tests/cron/test_cron_relay_delivery_guards.py

@@ -46,7 +46,7 @@ class TestOriginThreadStaleGuard:
                           "thread_id": SYNTH}}
         target = _resolve_single_delivery_target(job, "origin")
         assert target == {"platform": "slack", "chat_id": "D0BJTDCSR7C",
-                          "thread_id": None}
+                          "thread_id": None, "_resolved_from": "origin"}
 
     def test_origin_thread_kept_when_chat_not_home(self, monkeypatch):
         """A non-home Slack origin thread may be a genuine working thread: keep it."""