Enhancement: replace use of "official" yet unmaintained GitHub Actions

[Lovell Fuller]

A couple of official, GitHub-provided Actions that this repo uses have recently been flagged as unmaintained, which is a somewhat unexpected move from GitHub.

• actions/create-release - see actions/create-release#120
• actions/upload-release-asset - see actions/upload-release-asset#79

https://github.com/ncipollo/release-action looks like it provides everything we need, so that's a good place to start.