update runtime #23
Description
As can be seen in https://github.com/adam-p/danforth-east/blob/b07592ffabccc57418e72eac494e616c974051ed/app.yaml#L1, our runtime is python38. According to the runtime support schedule, python38 stops being supported in October 2024. We should update before then.
(On other projects I have recently had trouble with updates to Python 3.12, so I think we should go to python311.)