Comment 2 for bug 2012700

just to add another point to this bug, i tried with python juju==3.1.0.1

```python
    for app_name, app in model.applications.items():
        log.info(f"Upgrading {app_name} from {app.charm_url} to --channel={channel}")
        await app.refresh(channel=channel)
```

and found the same error is produced. I guess this likely indicates an issue on the controller