Fix typo in tox.ini (py13 => py313)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.10%. Comparing base (4eeea39) to head (05bf5f3).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #972 +/- ## ======================================= Coverage 91.10% 91.10% ======================================= Files 2 2 Lines 506 506 Branches 64 64 ======================================= Hits 461 461 Misses 27 27 Partials 18 18 ```

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