Deprecation warning when using pip_api on Python 3.11

[jamesclark-Zapata]

Reproduction

python3.11 -Wall  -c "import pip_api"
<snip>/lib/python3.11/site-packages/pip_api/_vendor/pyparsing.py:108: DeprecationWarning: module 'sre_constants' is deprecated
  import sre_constants

Root cause
sre_constants is imported by the vendored pyparsing module:

pip-api/pip_api/_vendor/pyparsing.py

Line 108 in 5ac3ec8

import sre_constants

see: python/cpython#91308

[di]

I took a shot at this in #196 but ran up against some unexpected test failures and haven't had a chance to take a closer look yet.