chore: update PostHog/.github pins

[marandaneto]

💡 Motivation and Context

Some workflows referenced older pinned PostHog/.github revisions. One older revision of the shared release approval workflow still used tag-based nested actions (actions/checkout@v6 and PostHog/posthog-github-action@v1.1.1), which violates the org policy requiring every action reference, including nested reusable workflow actions, to be pinned to a full-length commit SHA.

This updates all PostHog/.github reusable workflow/action references in this repository to the latest pinned PostHog/.github commit: 5fc4680761e8ac29a61b212756230eba0e276d8c.

💚 How did you test it?

• Ran git diff --check
• Verified all PostHog/.github references in .github point to 5fc4680761e8ac29a61b212756230eba0e276d8c
• Verified the latest PostHog/.github revision has no unpinned uses: references

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

If releasing new changes

• Ran pnpm changeset to generate a changeset file

[greptile-apps]

_{Reviews (1): Last reviewed commit: "chore: update PostHog/.github pins" | Re-trigger Greptile}