Summary

• make MAVEN_GPG_PASSPHRASE optional for Maven Central releases
• only add the gpg.passphrase Maven server entry when the secret value is present
• keep existing AWS secret storage and password-protected key support unchanged

Testing

• ruby -e 'require "yaml"; YAML.load_file(".github/workflows/maven_central_release.yml"); puts "workflow yaml ok"'
• git diff --check
• mvn -B -q -N -DforceStdout help:evaluate -Dexpression=project.version