Fix testcase for stream_input_type

tests/test_sse.py

@@ -280,6 +280,16 @@ def test_include_router_copies_stream_item_type():
     route = next(r for r in main_app.routes if r.path == "/stream_item_type")
     assert getattr(route, "stream_item_type", None) == Item
 
+    with TestClient(main_app) as client:
+        response = client.get("/stream_item_type")
+        assert response.status_code == 200
+        assert response.headers["content-type"] == "text/event-stream; charset=utf-8"
+        data_lines = [
+            line for line in response.text.strip().split("\n") if line.startswith("data: ")
+        ]
+        assert len(data_lines) == 1
+        assert '"name":"Plumbus"' in data_lines[0] or '"name": "Plumbus"' in data_lines[0]
+
 
 # Keepalive ping tests