Fix ruff error: remove unused BaseModel import

Author: jaschadub

symbiont/config.py

@@ -7,7 +7,7 @@
 from typing import Any, Dict, Optional, Union
 
 import yaml
-from pydantic import BaseModel, Field, field_validator
+from pydantic import Field, field_validator
 from pydantic_settings import BaseSettings, SettingsConfigDict