ci: Audit our github actions configs with zizmor

[bdarnell]

No description provided.

[github-advanced-security]

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[bdarnell]

Not merging this right now because I don't think the code scanning integration is the right interface for CI on PRs (it reported warnings without failing CI), but it might come back when there's a copy/pasteable config that has better output (and is faster. Installing zizmor from source takes longer than a full test run for us)