chore/ci: bump GitHub Actions to latest pinned versions (#1051)
Many of the actions in our workflows were several major versions behind
their current releases. Stale action versions miss security fixes,
runtime improvements, and node runtime upgrades that newer GitHub
runners increasingly require.
This bumps each action to the current latest stable major version while
keeping the existing pinning style (major-version tag for first-party
or well-known actions, full SHA for the third-party fuzz action).
Test Plan: CI on the resulting PR will exercise every updated workflow.