ci: pin GitHub Actions to commit SHAs

[roydahan]

Summary

• Pin all external GitHub Actions to full commit SHAs to reduce supply chain attack surface
• Upgrade outdated actions to their latest versions

This PR was generated automatically. Please verify that GitHub Actions work as expected with these changes before merging.

Reference: scylladb/scylladb#29421

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 354460b4-bfbf-40fb-8f51-a6724d4e813d

📥 Commits

Reviewing files that changed from the base of the PR and between 6317746 and 41f55bc.

📒 Files selected for processing (1)

• .github/workflows/main.yml

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📝 Walkthrough

Walkthrough

The PR updates the GitHub Actions workflow in .github/workflows/main.yml to pin core actions used in the build job to specific commit SHAs. Three actions were changed from floating major-version tags to pinned SHA references: actions/checkout, actions/setup-go, and actions/cache. The versions are updated to newer releases, and the existing step configuration including the checkout fetch-depth: '0' parameter is preserved.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'ci: pin GitHub Actions to commit SHAs' directly and clearly summarizes the main change in the pull request.
Description check	✅ Passed	The description explains the purpose of pinning GitHub Actions to commit SHAs for security and mentions upgrading actions, which aligns with the changeset.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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