Don't use naive datetime objects

tests/test_app.py

@@ -8,8 +8,10 @@ from fastapi.testclient import TestClient
 
 def is_roughly_now(datetime_str):
     """Check if a datetime string is roughly from now"""
-    now = dt.datetime.utcnow()
+    now = dt.datetime.now(dt.timezone.utc)
     datetime = dt.datetime.fromisoformat(datetime_str)
+    # set timezone, otherwise cannot subtract
+    datetime = datetime.replace(tzinfo=dt.timezone.utc)
     return (now - datetime).total_seconds() < 3