Update CI versions

Merge pull request #106 from jakkdl/followup_pr

version bump, detect stdlib import

release new version

Drop Python 3.7 and release

Use latest libcst (and black)

Ignore coverage bug on 38, 39

Release version 2023.4.1

Release version 2023.3.1

Release with calver

Require Black >= 23.1.0