Upgrade all third-party GitHub Actions and pin them to commit hashes

[Copilot]

This PR upgrades all of our third-party GitHub Actions to ensure they are compatible with the upcoming Node 20 deprecation.

While we're at it, we also switch all of our references to third-party actions to point to commit hashes, so as to protect ourselves from the the ongoing scourge of supply chain attacks against third-party actions. These supply chain attacks work by pushing malicious code to running tags like v2, which will then cause downstream workflows like ours to pull in the malicious code the next time they run.

For all of our third-party actions, I sourced the commit hashes by checking the Releases page for the most recent release and copying the commit hash of that release. I also added inline comments indicating the version number that corresponds to the commit hash.

Test workflows to confirm these upgrades don't break anything:

• pre-commit: https://github.com/ccao-data/ptaxsim/actions/runs/26308747272/job/77453411865
• R-CMD-check: https://github.com/ccao-data/ptaxsim/actions/runs/26308747264
• test-coverage: https://github.com/ccao-data/ptaxsim/actions/runs/26308747365
• pkgdown: https://github.com/ccao-data/ptaxsim/actions/runs/26308747360

Connects https://github.com/ccao-data/aws-infrastructure/issues/59.

[kyrasturgill]

This at a high level makes sense to me! Given that the checks are passing with these changes, I have no concerns or flags. Thank you for proactively protecting us from bad actors!