fix: harden GitHub Actions against supply chain attacks

[CybotTM]

Summary

• Pin all GitHub Actions references to immutable commit SHAs (prevents tag/branch force-push attacks)
• Add Dependabot configuration for automatic GitHub Actions version updates

Context

On 2026-03-19, aquasecurity/trivy-action was compromised via a tag force-push attack that exfiltrated secrets from CI runners. SHA-pinning prevents this class of attack entirely.

The netresearch org now enforces sha_pinning_required=true — workflows using tag/branch references will fail.

Ref: netresearch/ofelia#535

Test plan

• Verify CI passes with SHA-pinned actions
• Verify Dependabot creates PRs for action updates

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the security of GitHub Actions workflows by pinning action references to specific commit SHAs, mitigating the risk of supply chain attacks. It also configures Dependabot for automatic action updates and enforces organizational security policies.

Highlights

• Security Hardening: This PR pins GitHub Actions references to immutable commit SHAs to prevent against tag/branch force-push attacks, addressing a critical supply chain security concern.
• Dependabot Configuration: It introduces a Dependabot configuration for automatic updates of GitHub Actions versions, ensuring timely security updates.
• Organizational Policy: The changes align with the netresearch organization's policy of enforcing sha_pinning_required=true, which will cause workflows using tag/branch references to fail if not updated.

Ignored Files

• Ignored by pattern: .github/workflows/** (1)
  • .github/workflows/documentation.yml

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[gemini-code-assist]

Code Review

This pull request adds a Dependabot configuration for GitHub Actions. The configuration is a good start, but I've suggested an improvement to better manage version updates by separating major releases. More importantly, the PR description mentions pinning actions to commit SHAs, but those changes are not present. To fully address the security concerns, the action pinning changes should be included in this PR.

[gemini-code-assist]

Consider specifying update-types within your group to separate major version updates from minor and patch updates. Grouping all updates together can be problematic if a breaking change in one action's major update blocks the deployment of a simple patch for another. By creating separate PRs for major updates, you can handle them with more care and review them more thoroughly.

        patterns:
          - "*"
        update-types:
          - "minor"
          - "patch"

[Copilot]

Pull request overview

This PR hardens the repository’s GitHub Actions setup against tag/branch force-push supply chain attacks by switching to immutable action references and enabling automated upkeep via Dependabot.

Changes:

• Pin actions/checkout in the documentation workflow to a commit SHA.
• Add a Dependabot configuration to check for GitHub Actions updates weekly (with grouping enabled).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
.github/workflows/documentation.yml	Replaces the actions/checkout@v4 tag reference with a pinned commit SHA to prevent tag force-push attacks.
.github/dependabot.yml	Adds Dependabot config to automate GitHub Actions update PRs on a weekly schedule.

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[CybotTM]

Closing: fork, not actively maintained.