[CI] Upgrade GitHub Actions to v4

[Divyadarshee]

Summary

Upgrade GitHub Actions workflows to use v4 versions of deprecated actions.

Motivation

The CI workflows currently use deprecated versions of GitHub Actions that have reached end-of-life:

• actions/checkout@v3
• actions/upload-artifact@v3

These versions are no longer maintained by GitHub and should be upgraded to their actively supported v4 counterparts to:

1. Ensure CI/CD pipeline stability
2. Use secure, maintained versions of these critical workflow actions
3. Prevent potential failures from deprecated action versions

Details

This is a routine infrastructure maintenance task to keep the GitHub Actions in .github/workflows/ current with GitHub's recommendations.

Files affected

• .github/workflows/ci-sage.yml and .github/workflows/main.yml - all workflow files using v3 actions will be updated to v4

[Divyadarshee]

@jaraco - I noticed that the CI workflows are using deprecated GitHub Actions v3 versions (actions/checkout@v3 and actions/upload-artifact@v3), which have reached end-of-life. This is leading to recent CI failures in the build . I've prepared a PR to upgrade these to v4. Please let me know if there are any specific considerations I should be aware of, or if I should proceed differently.

[jaraco]

The code for these concerns originates from the skeleton project. Unfortunately, I can't transfer the issue there. Please send the PR there. Thanks.