chore: prepare for release 6.3.2

[aucampia]

Summary of changes

Prep for next release.

Checklist

• Checked that there aren't other open pull requests for
  the same change.
• Checked that all tests and type checking passes.
• Considered granting push permissions to the PR branch,
  so maintainers can fix minor issues and keep your PR up to date.

[coveralls]

Coverage: 90.838%. Remained the same when pulling 347e06f on aucampia:iwana-20230326T1301-release_6.3.2 into af17916 on RDFLib:main.