Use explicit Python version to suppress warning

[rtibbles]

Summary

Currently the pypi upload action gives a warning:
The python-versioninput is not set. The version of Python currently inPATH will be used.

This sets an explicit (but flexible) Python version to get the same effect as current, but suppress the warning.

References

https://github.com/actions/setup-python/blob/main/docs/advanced-usage.md#using-the-python-version-input

Reviewer guidance

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Testing checklist

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Critical and brittle code paths are covered by unit tests

PR process

• PR has the correct target branch and milestone
• PR has 'needs review' or 'work-in-progress' label
• If PR is ready for review, a reviewer has been added. (Don't use 'Assignees')
• If this is an important user-facing change, PR or related issue has a 'changelog' label
• If this includes an internal dependency change, a link to the diff is provided

Reviewer checklist

• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[github-actions]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.18.0.dev0_git.20241106204433.pex
Windows Installer (EXE)	kolibri-0.18.0.dev0+git.20241106204433-windows-setup-unsigned.exe
Debian Package	kolibri_0.18.0.dev0+git.20241106204433-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.18.0.dev0+git.20241106204433.dmg
Android Package (APK)	kolibri-0.18.0.dev0+git.20241106204433-0.1.4-debug.apk
TAR file	kolibri-0.18.0.dev0+git.20241106204433.tar.gz
WHL file	kolibri-0.18.0.dev0+git.20241106204433-py2.py3-none-any.whl