fix(ci): use GitHub App token in changelog update workflow

[j-d-ha]

Summary

• Fixes "cannot approve your own pull request" error in the update-changelog workflow
• The PR created by peter-evans/create-pull-request was authored by github-actions[bot] (via GITHUB_TOKEN), so the approval step — also using GITHUB_TOKEN — was rejected by GitHub as a self-approval
• Adds a actions/create-github-app-token step to generate a token from a dedicated GitHub App (CHANGELOG_UPDATE_ID / CHANGELOG_UPDATE_PRIVATE_KEY secrets), which authors the PR as the App bot instead
• The approval step continues to use GITHUB_TOKEN (github-actions[bot]), now a different actor from the PR author — so the approval succeeds

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✅ Checklist

• My changes build cleanly
• I've added/updated relevant tests
• I've followed the coding style for this project
• I've tested the changes locally (if applicable)

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🧪 Related Issues or PRs

N/A

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💬 Notes for Reviewers

Requires CHANGELOG_UPDATE_ID and CHANGELOG_UPDATE_PRIVATE_KEY repo secrets to be set before this workflow will work end-to-end.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@           Coverage Diff           @@
##             main     #312   +/-   ##
=======================================
  Coverage   87.38%   87.38%           
=======================================
  Files         113      113           
  Lines        2814     2814           
  Branches      351      351           
=======================================
  Hits         2459     2459           
  Misses        254      254           
  Partials      101      101           

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