WIP: [ci] update GitHub Actions

[jameslamb]

Updates some third-party GitHub Actions to their latest versions, to resolve warnings like this:

Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: actions/checkout@v3. For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.

Which can be seen in summaries like this: https://github.com/microsoft/LightGBM/actions/runs/8904974495?pr=6391

Notes for Reviewers

I found these like this:

git grep 'uses:'

The things changed in this PR are the only ones with new releases... except for r-lib/actions/setup-pandoc, which I'm scared to update and think we should leave untouched until we have a specific version to update it 😬

[borchero]

Shall we set up dependabot for this repo to get these updates automatically in a regular interval?

[jameslamb]

Sure, I'm open to trying that if you'd like to pursue it @borchero

[jameslamb]

hey cool, dependabot just opened a PR with similar changes!

#6453

Nice work @borchero ! Let's close this and go work over there.