docs: use client-id secret name for the releaser app in the maintainers guide

[zimeg]

Changelog

N/A — maintainer docs only, no user-facing change.

Summary

This pull request updates the maintainers guide so its releaser-app credentials list matches the secret names the workflows actually use.

• ci: use client-id instead of deprecated app-id for cli releaser github app #639 switched .github/workflows/release.yml and dependencies.yml from app-id: ${{ secrets.GH_APP_ID_RELEASER }} to client-id: ${{ secrets.GH_APP_CLIENT_ID_RELEASER }} (following create-github-app-token's app-id deprecation).
• The "Credentials and secrets" section still listed the deprecated GH_APP_ID_RELEASER, leaving docs and workflows out of sync.
• Anyone bootstrapping the releaser app from this guide (fork, key rotation, new environment) would set the wrong secret name and hit an empty client-id at runtime.

Preview

N/A — text-only doc change.

Testing

• grep -rn GH_APP_ID_RELEASER .github/ returns no matches; GH_APP_CLIENT_ID_RELEASER now appears in the guide and both workflows.

Notes

• Follow-up (tracked separately, out of scope here): once a release/dependencies run succeeds on GH_APP_CLIENT_ID_RELEASER, the now-unreferenced GH_APP_ID_RELEASER repo secret should be deleted to keep the secret surface tidy.

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.25%. Comparing base (b5982b9) to head (3114204).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #640      +/-   ##
==========================================
- Coverage   72.26%   72.25%   -0.01%     
==========================================
  Files         238      238              
  Lines       20072    20072              
==========================================
- Hits        14505    14503       -2     
- Misses       4298     4299       +1     
- Partials     1269     1270       +1     

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