Pin infra reusable workflows to immutable SHA and add pull_request_target fork guards

[Copilot]

📌 Fixes

Issue linking is handled automatically by the system.

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📝 Summary of Changes

This PR replaces mutable kubestellar/infra reusable workflow refs with an immutable commit SHA and hardens pull_request_target execution paths against fork-originated PRs.
Scope is limited to workflow security and reference integrity in .github/workflows.

• Workflow pinning
  • Pinned all specified reusable workflow uses: references from @main to:
    • @a160acca0bdce1ac6c649e006d680d5f6d53024e # main
• Fork execution guards
  • Added a strict same-repo guard to copilot-automation job.
  • Added an event-aware guard to ai-fix job so pull_request_target only runs for same-repo PRs.
• Permission hardening
  • Added explicit permissions in copilot-dco.yml to satisfy workflow security policy (contents: read, pull-requests: write).

jobs:
  ai-fix:
    if: github.event_name != 'pull_request_target' || github.event.pull_request.head.repo.full_name == github.repository
    uses: kubestellar/infra/.github/workflows/reusable-ai-fix.yml@a160acca0bdce1ac6c649e006d680d5f6d53024e  # main

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Changes Made

• Updated all targeted kubestellar/infra reusable workflow refs to immutable SHA pins.
• Refactored workflow job guards for secure pull_request_target handling in copilot-automation.yml and ai-fix.yml.
• Fixed missing explicit permissions in copilot-dco.yml to align with workflow security scanning.
• Added tests for workflow behavior (not applicable for reusable workflow reference/guard-only changes).

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Checklist

Please ensure the following before submitting your PR:

• I have reviewed the project's contribution guidelines.
• I have performed a self-review of my changes.
• I have written unit tests for the changes (if applicable).
• I have updated the documentation (if applicable).
• I have tested the changes locally and ensured they work as expected.
• All CI checks are passing.

Security Considerations

If this PR modifies any security-sensitive files, confirm:

• Dockerfiles — verified base images, avoided running as root
• Kubernetes manifests — checked RBAC permissions and secrets handling
• CI/CD workflows — inspected for command injection or credential exposure
• Dependencies — validated new packages, checked for known vulnerabilities
• Security configs — changes align with project security policies

Leave unchecked if not applicable. See CONTRIBUTING.md for details.

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Screenshots or Logs (if applicable)

N/A (workflow YAML-only changes).

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👀 Reviewer Notes

• This PR intentionally updates only the workflows listed in the issue scope.
• SHA annotations keep # main for traceability while enforcing immutable refs.

Original prompt

Pin all kubestellar/infra reusable workflow references from mutable @main to immutable commit SHA a160acca0bdce1ac6c649e006d680d5f6d53024e, and add fork guards to workflows using pull_request_target.

Fixes #5940 - Pin kubestellar/infra workflows to SHA
Fixes #5941 - Add fork guard to copilot-automation.yml
Fixes #5949 - Add fork guard to ai-fix.yml

Required Changes:

1. Pin all workflow files to SHA a160acca0bdce1ac6c649e006d680d5f6d53024e:

Replace @main with @a160acca0bdce1ac6c649e006d680d5f6d53024e # main in these files:

• .github/workflows/stale.yml (line with kubestellar/infra/.github/workflows/reusable-stale.yml@main)
• .github/workflows/feedback.yml (line with kubestellar/infra/.github/workflows/reusable-feedback.yml@main)
• .github/workflows/label-helper.yml (line with kubestellar/infra/.github/workflows/reusable-label-helper.yml@main)
• .github/workflows/add-help-wanted.yml (line with kubestellar/infra/.github/workflows/reusable-add-help-wanted.yml@main)
• .github/workflows/greetings.yml (line with kubestellar/infra/.github/workflows/reusable-greetings.yml@main)
• .github/workflows/copilot-dco.yml (line with kubestellar/infra/.github/workflows/reusable-copilot-dco.yml@main)
• .github/workflows/scorecard.yml (line with kubestellar/infra/.github/workflows/reusable-scorecard.yml@main)
• .github/workflows/assignment-helper.yml (line with kubestellar/infra/.github/workflows/reusable-assignment-helper.yml@main)
• .github/workflows/pr-verifier.yml (line with kubestellar/infra/.github/workflows/reusable-pr-verifier.yml@main)
• .github/workflows/copilot-automation.yml (line with kubestellar/infra/.github/workflows/reusable-copilot-automation.yml@main)
• .github/workflows/ai-fix.yml (line with kubestellar/infra/.github/workflows/reusable-ai-fix.yml@main)

2. Add fork guard to copilot-automation.yml:

In the copilot-automation job, add this line immediately after copilot-automation::

    if: github.event.pull_request.head.repo.full_name == github.repository

3. Add fork guard to ai-fix.yml:

In the ai-fix job, add this line immediately after ai-fix::

    if: github.event_name != 'pull_request_target' || github.event.pull_request.head.repo.full_name == github.repository

Example of expected result for copilot-automation.yml:

jobs:
  copilot-automation:
    if: github.event.pull_request.head.repo.full_name == github.repository
    uses: kubestellar/infra/.github/workflows/reusable-copilot-automation.yml@a160acca0bdce1ac6c649e006d680d5f6d53024e  # main

Example of expected result for ai-fix.yml:

jobs:
  ai-fix:
    if: github.event_name != 'pull_request_target' || github.event.pull_request.head.repo.full_name == github.repository
    uses: kubestellar/infra/.github/workflows/reusable-ai-fix.yml@a160acca0bdce1ac6c649e006d680d5f6d53024e  # main

Create all changes on branch scanner/fix-5940.

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