New check: find pypa/gh-action-pypi-publish@master

[nedbat]

This message can happen:

You are using "pypa/gh-action-pypi-publish@master". The "master" branch of this project has been sunset and will not receive any updates, not even security bug fixes. Please, make sure to use a supported version. If you want to pin to v1 major version, use "pypa/gh-action-pypi-publish@release/v1". If you feel adventurous, you may opt to use use "pypa/gh-action-pypi-publish@unstable/v1" instead. A more general recommendation is to pin to exact tags or commit shas.

Add a check that identifies workflows using this branch of this action.