Parent-pom 12 is modified to generate .sha512 checksums. Due to a bug in the rules for repository.apache.org, these cannot be uploaded unless they (the checksums) are gpg-signed. Although there's an issue to fix this
INFRA-14923 , the work is currently stalled.
In the meantime, modify the parent-pom to gpg sign and attach the signatures, for .sha512 checksums.