Install Twine to upload to PyPI

[hugovk]

Follow on from #491, to fix https://github.com/ultrajson/ultrajson/actions/runs/1578092423.

Changes proposed in this pull request:

• Install Twine to upload to PyPI
• Also cache pip

[codecov-commenter]

Codecov Report

Merging #492 (243d49b) into main (269621b) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #492   +/-   ##
=======================================
  Coverage   88.96%   88.96%           
=======================================
  Files           6        6           
  Lines        1685     1685           
=======================================
  Hits         1499     1499           
  Misses        186      186           

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[hugovk]

First deploy to Test PyPI after merge had a 6h timeout when testing a wheel for one of the jobs ("build-QEMU-emulated-wheels (aarch64, pp38)"):

https://github.com/ultrajson/ultrajson/actions/runs/1579780947/attempts/1

Restarting and it completed:

https://github.com/ultrajson/ultrajson/actions/runs/1579780947

-->

https://test.pypi.org/project/ujson/4.3.1.dev8/#files ✅

Will do a full release later.