feat(action): add ca_bundle input for custom CA certificates on self-hosted runners

[GG-HH]

Summary

• Adds a new optional ca_bundle input to actions/secret/action.yml that accepts a path to a CA bundle file relative to the repository root
• Maps INPUT_CA_BUNDLE → REQUESTS_CA_BUNDLE in docker/actions-secret-entrypoint.sh before ggshield starts, so all HTTPS requests honour the provided CA
• Adds two functional tests that spin up a real local HTTPS server signed by a custom CA and verify the fix end-to-end inside the actual Docker container

Motivation

Self-hosted runners that route HTTPS traffic through a corporate proxy or firewall present a CA certificate not included in the python:3.10-slim trust store baked into the action image. This causes ggshield to fail with CERTIFICATE_VERIFY_FAILED on every run. Providing a CA bundle path resolves this without requiring users to rebuild the image.

Test plan

• uv run --with pytest pytest tests/functional/test_github_action_ca_bundle.py -v — both tests pass
• test_ssl_fails_without_ca_bundle confirms SSL fails when no CA bundle is set
• test_ssl_succeeds_with_ca_bundle confirms SSL succeeds when INPUT_CA_BUNDLE=ca.crt is set
• Tests are skipped automatically if Docker or openssl are not available

Usage

- uses: GitGuardian/ggshield-action@v1
  with:
    ca_bundle: certs/corporate-ca.crt
  env:
    GITGUARDIAN_API_KEY: ${{ secrets.GITGUARDIAN_API_KEY }}

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.51%. Comparing base (158ff03) to head (dda3649).
⚠️ Report is 25 commits behind head on main.

Additional details and impacted files

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##             main    #1300   +/-   ##
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  Coverage   93.51%   93.51%           
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  Files         189      189           
  Lines       11081    11081           
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  Hits        10362    10362           
  Misses        719      719           

Flag	Coverage Δ
unittests	93.51% <ø> (ø)

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