fix: replace datetime.UTC with timezone.utc for Python 3.10 compat

datetime.UTC was introduced in Python 3.11. timezone.utc is available
since Python 3.2 and is functionally identical.

Co-Authored-By: Zindello <josh@zindello.com.au>

repeater/web/api_endpoints.py

@@ -2,13 +2,7 @@ import json
 import logging
 import os
 import time
-from datetime import datetime
-
-try:
-    from datetime import UTC
-except ImportError:
-    from datetime import timezone
-    UTC = timezone.utc
+from datetime import datetime, timezone
 from pathlib import Path
 from typing import Callable, Optional
 
@@ -5256,7 +5250,7 @@ class APIEndpoints:
             exported = _sanitize(exported)
 
             meta = {
-                "exported_at": datetime.now(UTC).isoformat().replace("+00:00", "Z"),
+                "exported_at": datetime.now(timezone.utc).isoformat().replace("+00:00", "Z"),
                 "version": __version__,
                 "config_path": self._config_path,
                 "includes_secrets": full_backup,