Add ruby 3.1 / 3.2 to test matrix + fix failing GH action tests for 2.6 / 2.7

[maxwofford]

Hey all! Thanks so much for maintaining this wonderful gem for so long. Going through this because we're upgrading to ruby 3 soon & were checking out some of our own projects.

The changes are best reviewed by commit. tl;dr:

• standardrb linter was failing in GH actions, so this ran the auto-formatter + included a manual fix
• Ruby 3.1 & 3.2 are now in the GH action test matrix (and pass)

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These changes are mostly changes to CI and formatting. No expected change in the interfaces, so I recommend releasing this as a patch (1.4.1). EDIT: Looks like there are a couple changes since the last tagged release, so ignore what I said about 1.4.1.

[jasonlong]

Thanks @maxwofford. I'll go ahead and get this merged and see about creating a release to capture everything that's been done over the past several years.