ci: use python from the correct path
ci: use python from the correct path

Apparently the old path we were using for Python 2 on Windows was not
documented, and eventually got removed. This switches our CI to use the
correct path.

aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust