Add support for Python 3.13

[hugovk]

Type of changes

• Bug fix
• New feature
• Documentation / docstrings
• Tests
• Other

Checklist

• I've run the latest black with default args on new code.
• I've updated CHANGELOG.md and CONTRIBUTORS.md where appropriate.
• I've added tests for new code.
• I accept that @willmcgugan may be pedantic in the code review.

Description

The final Python 3.13 release candidate is out now! 🚀

The Release Manager has issued a call to action:

We strongly encourage maintainers of third-party Python projects to prepare their projects for 3.13 compatibilities during this phase, and where necessary publish Python 3.13 wheels on PyPI to be ready for the final release of 3.13.0. Any binary wheels built against Python 3.13.0rc2 will work with future versions of Python 3.13. As always, report any issues to the Python bug tracker.

This PR adds 3.13 to the CI and tox, and fixes a test that fails on 3.13.

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.25%. Comparing base (9c74f03) to head (c8abbb3).
Report is 4 commits behind head on master.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3481   +/-   ##
=======================================
  Coverage   98.25%   98.25%           
=======================================
  Files          74       74           
  Lines        8072     8072           
=======================================
  Hits         7931     7931           
  Misses        141      141           

Flag	Coverage Δ
unittests	98.25% <ø> (ø)

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[willmcgugan]

Thank you! Will do a release soon.