Update for Windows platform. Resolves #18096

[ag-tafe]

Fixes #18096

Update of CONTRIBUTING.md document to be able to run tests using Windows OS.

python3 runtests.py

Change to:

python runtests.py

# Use mypy to check mypy's own code
python3 runtests.py self
# or equivalently:
python3 -m mypy --config-file mypy_self_check.ini -p mypy

Change to:

# Use mypy to check mypy's own code
python runtests.py self
# or equivalently:
python -m mypy --config-file mypy_self_check.ini -p mypy

described above to install tox via pip (e.g., python3 -m pip install tox).

Change to:
described above to install tox via pip (e.g., python -m pip install tox).

[sobolevn]

Is this specific to your setup? I haven't heard about python3 being a problem on Windows before.

[AlexWaygood]

I was a Windows programmer for several years -- I can confirm that most Python installations on Windows typically come with a python.exe executable but not a python3.exe executable

[JelleZijlstra]

The flip side is that on my Mac:

$ python -V
-bash: python: command not found
$ python3 -V
Python 3.13.0

But maybe we can just expect contributors to figure that out.

[hauntsaninja]

The instructions still say this for non-Windows, so Mac should be fine:

python3 -m venv venv
source venv/bin/activate