Actual publishing to maven central is done outside of this project based on the build artifacts published for a release to GitHub Packages (so they are not build again). This is done to ensure secrecy of the password to OSSRH and the required GPG/PGP signatures. (see also https://central.sonatype.org/pages/requirements.html)
OSSRH configuration included in gradle to simplify SNAPSHOT releases in case they are needed. Would be available under https://oss.sonatype.org/content/groups/public/
https://oss.sonatype.org/content/groups/public/