python: upstream merge v2025.20.0

[austin3dickey]

New version number

https://github.com/microsoft/vscode-python/releases/tag/v2025.20.0

microsoft/vscode-python@v2025.18.0...v2025.20.0

• dependency upgrades including PET, which I think affects the handoff of uv environments from PET to this extension, so we need to double-check that
• fixes to python test collection and reporting
• some changes to terminal code execution
• a bugfix to selecting interpreters?

Checklist

• Merge upstream changes
• If needed, match CI changes from upstream merge into Positron's .github/workflows/positron-python-ci.yml
• Run Build Python Environment Tools Release workflow in the positron-builds repo to check for and build latest PET releases
• If new PET release, update version number in package.json, under positron -> pet
• Update dependencies in python_files/posit/pinned-test-requirements.txt
• Run scripts/pip-compile-ipykernel.py to update python_files/ipykernel_requirements/{py3,cp3,cpx}-requirements.txt
• Follow the instructions in python_files/positron_requirements/requirements.in to update python_files/positron_requirements/requirements.txt

[juliasilge]

It would be good to get this done before we all leave for the holidays.