Publish swh-graph to PyPI

Since fc58f8b0d597ee10c82051bf6bbbe7706bbc5879, builds of the public documentation fails because it can't install swh-graph from PyPI: https://jenkins.softwareheritage.org/view/all/job/DDOC/job/publish/253/console

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Migrated from T1943 (view on Phabricator)