Fix GPG secret naming inconsistency in publishing documentation

[Copilot]

The CI/CD setup section referenced secrets.GPG_KEY_ID in the workflow example but didn't list it as a required secret.

Changes:

• Added GPG_KEY_ID to the list of required GitHub repository secrets with example format

The documentation now correctly lists all five secrets used in the workflow:

env:
  ORG_GRADLE_PROJECT_signingKeyId: ${{ secrets.GPG_KEY_ID }}  # Now documented
  ORG_GRADLE_PROJECT_signingKey: ${{ secrets.GPG_SIGNING_KEY }}
  ORG_GRADLE_PROJECT_signingPassword: ${{ secrets.GPG_SIGNING_PASSWORD }}

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[Copilot]

Pull request overview

This PR fixes a documentation inconsistency in the publishing guide where the workflow example referenced secrets.GPG_KEY_ID (line 188) but this secret was not listed in the required secrets section above.

Key Changes:

• Added GPG_KEY_ID to the list of required GitHub repository secrets in the CI/CD Setup section
• Included format example "(the key ID, e.g., ABCD1234)" consistent with the documentation style for other secrets

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