pmd: 6.14.0 -> 6.15.0 (#62503)

* pmd: 6.14.0 -> 6.15.0

Semi-automatic update generated by
https://github.com/ryantm/nixpkgs-update tools. This update was made
based on information from
https://repology.org/metapackage/pmd/versions

* pmd: cleanup