Assume naive datetimes are UTC in the msgpack and cbor2 converters - #775

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@v4, gacts/run-and-post-run@4683764dd706df847f57b9bed39d08164bcd2690. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/