Solve alleged twine warnings on pypi publishing

[echedey-ls]

• [ ] Closes #xxxx
• I am familiar with the contributing guidelines
• [ ] Tests added
• [ ] Updates entries in docs/sphinx/source/reference for API changes.
• [ ] Adds description and name entries in the appropriate "what's new" file in docs/sphinx/source/whatsnew for all changes. Includes link to the GitHub Issue with :issue:`num` or this Pull Request with :pull:`num`. Includes contributor name and/or GitHub username (link with :ghuser:`user`).
• [ ] New code is fully documented. Includes numpydoc compliant docstrings, examples, and comments where necessary.
• Pull request is nearly complete and ready for detailed review.
• Maintainer: Appropriate GitHub Labels (including remote-data) and Milestone are assigned to the Pull Request and linked Issue.

I'm pretty sure the following warnings are being raised in the publish action, since metadata verification is not disabled in the PyPI publishing action. Can't compare against last publication as the logs were deleted.
(I was playing with the sdist and installation procedures, in case you were wondering). See comments below.

(venv) PS C:\...\pvlib-python> py -m twine check dist/*
Checking dist\pvlib-0.9.6.dev25+g763dd0a.d20230618-py3-none-any.whl:
PASSED with warnings WARNING  `long_description_content_type` missing. defaulting to `text/x-rst`.
Checking dist\pvlib-0.9.6.dev25+g763dd0a.d20230618.tar.gz:
PASSED with warnings WARNING  `long_description_content_type` missing. defaulting to `text/x-rst`.

This solves it. It currently does not have any impact but just in case.

[echedey-ls]

I'd keep this open until the warning can be confirmed on v0.10 release.

[echedey-ls]

From last release logs, at Publish distribution to PyPi, lines 16 to 19:

Checking dist/pvlib-0.10.0-py3-none-any.whl: PASSED with warnings
WARNING  `long_description_content_type` missing. defaulting to `text/x-rst`.   
Checking dist/pvlib-0.10.0.tar.gz: PASSED with warnings
WARNING  `long_description_content_type` missing. defaulting to `text/x-rst`.

[kandersolar]

Thanks @echedey-ls! Would it make sense to add python -m twine check dist/* to the CI build job (after this step) so that we can check for these types of warnings between releases?

[echedey-ls]

I don't really have the knowledge to say so. I believe the desired behaviour would be to report the warnings on the action status although I don't have a clue on how to do that or if GitHub automatically does. From linked action recommendation on metadata verification:

It is recommended that you run twine check just after producing your files, but this also runs twine check before upload. You can also disable the twine check with:

with:
     verify-metadata: false

So I'd say yes. I'll add that and revert if you think so later.

[echedey-ls]

BTW, I don't have a clue on how to test this.

[echedey-ls]

It amazes me how you review everything with such depth. I wouldn't have spotted the text/plain rendering.

[kandersolar]

LGTM. Thanks @echedey-ls, it's great to have another person looking at the project's infrastructure like this!

[kandersolar]

Whoops, looks like this one got forgotten. I'll go ahead and merge now. Thanks again @echedey-ls!