ci: Keep GITHUB_TOKEN off disk when checking out PR code

[mariiapisarenko]

What

Adds persist-credentials: false to both PR-head checkouts in os-extension-test.yml. These check out fork-controlled code in a job that holds vault secrets, and actions/checkout otherwise leaves the token in .git/config where the Maven build could read it.

Why

Part of TECHOPS-525.
Minimal, non-breaking defense-in-depth behind the caller's environment gate.

[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: 06c8e300-59b2-410e-ab71-5b65f3a09a3c

📥 Commits

Reviewing files that changed from the base of the PR and between 991cd0a and 2699635.

📒 Files selected for processing (1)

• .github/workflows/os-extension-test.yml

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📝 Walkthrough

Walkthrough

The workflow disables persisted Git credentials in the build and unit-test checkout steps. Comments document the defense-in-depth rationale.

Changes

Checkout credential handling

Layer / File(s)	Summary
Secure workflow checkouts .github/workflows/os-extension-test.yml	Build and unit-test checkout steps set persist-credentials: false and include explanatory comments.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Mergeability Score: ⚪ Minimal · up to 26996

The workflow now avoids persisting GITHUB_TOKEN credentials during fork-controlled checkouts, with no actionable merge-blocking risk remaining after normal checks.

Suggested reviewers: jandroav, sayalim0412

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely identifies the primary CI security change: preventing GITHUB_TOKEN persistence during PR code checkout.
Description check	✅ Passed	The description directly explains the checkout changes, security purpose, affected workflow, and related tracking issue.
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.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch harden-fork-pr-checkout

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