False positive of WARNING found in tests

I have a test that is sometimes failing with:

```
Error: error waiting for shutdown

Caused by:
channel lagged by 1
=========================== short test summary info ============================
ERROR tests/test_sling.py::test_gossip - ValueError:
Node errors:
- lightningd-2: had warning messages
```

I don't know why that happens or what it means but it started somewhat recently and i believe it is falsely triggered by:

```
lightningd-2 2025-09-08T03:49:22.049Z INFO 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-connectd: Received WIRE_WARNING: WARNING: channel_announcement: no unspent txout 106x4x0
```

Where it finds the ` WARNING:` search term in the middle of the log instead of where the log level is.