[Bug] Benign log is reported as ERROR

## 🐛 Bug Report

On v4.7.0 60.000 ERRORs are printed per hour of the type:
```
Failed to fetch previous certificate — Certificate with this author for round 38161972 already exists in storage
Failed to fetch previous certificate — Certificate for round 38161972 already exists in storage (gc = 38161866)
```
