fix: update python-publish to use python 3.9

[github-actions[bot]]

Python Tests

    6 files  ±0  168 suites  ±0   3s :stopwatch: ±0s   89 tests ±0    89 :heavy_check_mark: ±0  0 :zzz: ±0  0 :x: ±0  429 runs  ±0  429 :heavy_check_mark: ±0  0 :zzz: ±0  0 :x: ±0 

Results for commit b268eff5. ± Comparison against base commit bbf51422.

[github-actions[bot]]

Python Tests

    6 files  ±0  168 suites  ±0   3s :stopwatch: ±0s   89 tests ±0    89 :heavy_check_mark: ±0  0 :zzz: ±0  0 :x: ±0  429 runs  ±0  429 :heavy_check_mark: ±0  0 :zzz: ±0  0 :x: ±0 

Results for commit 91bb97ca. ± Comparison against base commit bbf51422.

[AdamMinton]

Publish to pypi can be done manually, going to close and release this as chore to avoid incremental version