change of the datetime implementation

Web/app.py

@@ -1217,6 +1217,12 @@ def create_return_reminders_admin():
             start_dt = borrow_doc.get('Start')
             end_dt = borrow_doc.get('End')
 
+            if isinstance(start_dt, datetime.datetime) and start_dt.tzinfo is None:
+                start_dt = start_dt.replace(tzinfo=datetime.timezone.utc)
+
+            if isinstance(end_dt, datetime.datetime) and end_dt.tzinfo is None:
+                end_dt = end_dt.replace(tzinfo=datetime.timezone.utc)
+
             if isinstance(start_dt, datetime.datetime) and start_dt <= one_day_ago:
                 _create_notification(
                     db,