Harden CI with pinned action versions and Zizmor analysis

[kaylendog]

This PR hardens the various CI workflows in the repo.

• Updates actions to latest available versions, since many were a few years out of date.
• Disables credential persistence by actions/checkout, since we don't do any pushing back to the remote.
• ⚠️ Disables caching for the release workflow.
• Uses the gh CLI in place of third-party actions.

Fixes #65

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[andybalaam]

Great, thanks!

[AndrewFerr]

For posterity, this PR left the release workflow in a unusable state, and had to be fixed by a few follow-up PRs:

• Fix environment setting in release workflow job #69
• Remove nonexistent "--draft" argument from "gh release upload" command #72
• Release v0.5.1 #75

So if a similar PR as this is made on other repos, findings from the above PRs should be taken into account.