Release 1.3.1

[bgilbert]

OpenSlide Python release process

• [x] Update CHANGELOG.md and version in openslide/_version.py
• [x] Create and push signed tag
• [x] git clean -dxf && mkdir dist
• [x] Find the workflow run for the tag; download its docs and wheels artifacts
• [x] unzip /path/to/downloaded/openslide-python-wheels.zip && mv openslide-python-wheels-*/* dist/
• [x] python setup.py sdist
• [x] twine upload dist/*
• [x] Recompress tarball with xz
• [x] Attach release notes to GitHub release; upload tarballs and wheels
• [x] cd into website checkout; rm -r api/python && unzip /path/to/downloaded/openslide-python-docs.zip && mv openslide-python-docs-* api/python
• [x] Update website: _data/releases.yaml, _includes/news.md
• [x] Update Ubuntu PPA
• [x] Send mail to -announce and -users
• [x] Update Fedora and EPEL packages
• [x] Update MacPorts package

[bgilbert]

Deferring PPA update until after OpenSlide 4.0.0, since we'll need to update the soname dependency.

[bgilbert]

MacPorts updated for the new release, but Flask and Pillow aren't packaged for 3.12 yet. The remaining MacPorts update is tracked in https://github.com/openslide/openslide-python/issues/223.