Fix DeprecationWarning from datetime.utcnow() use

Author: jiridanek

src/quart/helpers.py

@@ -4,7 +4,7 @@
 import os
 import pkgutil
 import sys
-from datetime import datetime, timedelta
+from datetime import datetime, timedelta, timezone
 from functools import lru_cache, wraps
 from io import BytesIO
 from pathlib import Path
@@ -348,7 +348,7 @@ async def send_file(
     response.cache_control.public = True
     if cache_timeout is not None:
         response.cache_control.max_age = cache_timeout
-        response.expires = datetime.utcnow() + timedelta(seconds=cache_timeout)
+        response.expires = datetime.now(timezone.utc) + timedelta(seconds=cache_timeout)
 
     if add_etags and etag is not None:
         response.set_etag(etag)

src/quart/sessions.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 import hashlib
-from datetime import datetime
+from datetime import datetime, timezone
 from typing import TYPE_CHECKING
 
 from flask.sessions import (  # noqa: F401
@@ -75,7 +75,7 @@ def get_expiration_time(self, app: Quart, session: SessionMixin) -> datetime | N
         the browser stops accessing the app.
         """
         if session.permanent:
-            return datetime.utcnow() + app.permanent_session_lifetime
+            return datetime.now(timezone.utc) + app.permanent_session_lifetime
         else:
             return None