[WIP] Support for Python 3.13

[pmisik]

Work in progress to see what needs to be fixed to be compatible with future Python 3.13.

Contributor Checklist:

• I have updated the unit tests
• I have created a file in the newsfragments directory (and read the README.txt in that directory)
• I have updated the appropriate documentation

[yan12125]

The first CI error seems related to a Pillow issue: python-pillow/Pillow#8050

I also got erros in other dependencies: cffi, greenlet, ruamel.yaml.clib, scandir. A tracking issue may be worthwhile for those dependencies.

[pmisik]

A tracking issue may be worthwhile for those dependencies.

Tracking issue #7631

[yan12125]

For Pillow, the relevant pull request is merged, and the exec branch is gone. Thus, git+https://github.com/radarhere/Pillow.git@exec can be replaced with git+https://github.com/python-pillow/Pillow.git.

[pmisik]

For Pillow, the relevant pull request is merged, and the exec branch is gone. Thus, git+https://github.com/radarhere/>Pillow.git@exec can be replaced with git+https://github.com/python-pillow/Pillow.git.

@yan12125 thanks for hint.
I've applied change.

Based on pillow issue tracker it seems we might expect release of compatible pillow package around July 1, 2024 python-pillow/Pillow#8076