Fix deprecated datetime.utcnow() and test assertion for clean_text

collectors/base.py

@@ -4,7 +4,7 @@ import tempfile
 import hashlib
 import logging
 from abc import ABC, abstractmethod
-from datetime import datetime
+import datetime
 from pathlib import Path
 from typing import Optional
 
@@ -119,7 +119,7 @@ class BaseCollector(ABC):
                     title=self._extract_title(url),
                     raw_path=final_path,
                     content_hash=content_hash,
-                    fetch_date=datetime.utcnow().isoformat(),
+                    fetch_date=datetime.datetime.now(datetime.timezone.utc).isoformat(),
                     etag=etag,
                     last_modified=last_modified,
                     char_count=len(content.decode('utf-8', errors='replace')),