community/py3-pikepdf: upgrade to 8.6.0

v8.5.3...v8.6.0 -> code changes lgtm

Changelog

v8.6.0
======

- Implemented Page.artbox and Page.bleedbox to access these page dimension boxes.

source: https://github.com/pikepdf/pikepdf/blob/1646930be087fa96e1fc0ba64bf29c68c4ca41d6/docs/releasenotes/version8.rst