Upgrade version of vendored package 'packaging' to support PEP 600

[xrogaan]

Issue description

PEP 600 introduce new tags relative to glibc. packaging has seen support for PEP 600 introduced some time after the release of 20.4, which is the current version vendored. Without the upgrade pipenv will at best try to compile the sdist, and at worse fail to do so, instead of installing the wheel.

It is currently impossible for pipenv to handle PyQt6, as the project follows the PEP 600 naming scheme.