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 significantly enhances the security posture of the repository's CI/CD workflows by implementing robust measures against supply chain attacks. It ensures that all GitHub Actions used are locked to specific, immutable commit SHAs, preventing malicious alterations via tag or branch force-pushes. Additionally, it establishes an automated system for keeping these actions up-to-date, maintaining both security and operational efficiency.

Highlights

• GitHub Actions Security: Pinned all GitHub Actions references to immutable commit SHAs to prevent tag/branch force-push attacks, addressing a critical supply chain vulnerability.
• Automated Updates: Introduced Dependabot configuration to automatically manage and update GitHub Actions versions, ensuring continuous security and functionality.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	/gemini review	Performs a code review for the current pull request in its current state.
Pull Request Summary	/gemini summary	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	/gemini help	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for GitHub and other Google products, sign up here.

Footnotes

1. Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

[gemini-code-assist]

Code Review

This pull request introduces a Dependabot configuration to automatically manage updates for GitHub Actions, which is a great step towards maintaining security and stability after pinning actions to specific SHAs. The configuration is well-structured. I've added one suggestion to further improve the workflow by automatically adding reviewers and labels to Dependabot's pull requests, which will help in managing these updates more efficiently.