SRE 696: Fix stale approvals reusable workflow checkout for PR callers

[lunelson]

Summary

• Always checkout the shared action from hashintel/.github instead of the PR head repository
• Remove the split checkout path added in Avoid dismissing approvals on restacks alone #58 for pull_request events
• Always resolve and use the reusable workflow ref as the checkout ref

Why

PR #58 made pull_request events checkout the PR head repository so changes to .github/actions/dismiss-stale-approvals could be self-tested before merge. That breaks callers in other repositories because their PR head checkout does not contain .github/actions/dismiss-stale-approvals/self-test.sh.

The reusable workflow should run the actual shared action from hashintel/.github regardless of which repository triggered the PR event. Now that this branch lives in hashintel/.github rather than a fork, the OIDC step can run on pull_request events and provide the exact workflow ref for checkout.

Linear

• SRE-696

Tests

• .github/actions/dismiss-stale-approvals/self-test.sh

[cursor]

PR Summary

Low Risk
Low risk: this only adjusts the reusable workflow’s checkout logic for a composite action, with no product code changes; main risk is mis-resolving the workflow ref and breaking the CI job.

Overview
Ensures the stale-approvals reusable workflow always checks out the dismiss-stale-approvals action from hashintel/.github (using the resolved reusable-workflow ref), instead of conditionally checking out the PR head repo on pull_request events.

Removes the split pull_request vs non-pull_request checkout paths so self-test.sh and the action are consistently sourced from the shared repository across callers.

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[augmentcode]

🤖 Augment PR Summary

Summary: Ensures the stale-approvals reusable workflow always checks out the shared dismiss-stale-approvals action from hashintel/.github.
Change: Removes the pull_request-specific checkout path and consistently resolves/uses the reusable-workflow ref for checkout.

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[augmentcode]

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