Deploy: Fix deprecation warning with pypa/gh-action-pypi-publish@master

[hugovk]

https://github.com/pypa/gh-action-pypi-publish#-master-branch-sunset- says:

The master branch version has been sunset. Please, change the GitHub Action version you use from master to release/v1 or use an exact tag, or a full Git commit SHA.

And there are warnings for example at https://github.com/python-twitter-tools/twitter/actions/runs/3051809874

So let's use pypa/gh-action-pypi-publish@release/v1

Also bump actions/checkout whilst we're here.

[coveralls]

Pull Request Test Coverage Report for Build 3053106032

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 31.316%

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Totals
Change from base Build 3051803496:	0.0%
Covered Lines:	652
Relevant Lines:	2082

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💛 - Coveralls