Fix CI ASV check by allowing any py 3.9.* for ubuntu-latest

[kandersolar]

• 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.

The "quick ASV check" CI job started failing yesterday: https://github.com/pvlib/pvlib-python/actions/runs/3597286595/jobs/6058885668

The job runs on ubuntu-latest, which as of yesterday refers to Ubuntu-22.04 instead of Ubuntu-20.04 (ref). The oldest patch version of python 3.9 available through setup-python for Ubuntu 22.04 is 3.9.12 (actions/setup-python#552 (comment)), so specifying 3.9.7 as the job currently does results in an error. I don't think the patch version really matters here, so I've unpinned the patch version to just require any 3.9 instead of specifically 3.9.7.

[AdamRJensen]

Seems reasonable 👍

[adriesse]

Thanks for looking into that!

[kandersolar]

Predicting no objections to what I think is a trivial change, I'll go ahead and merge this so other folks can get rid of the red X on their PRs.