Rollup merge of #70116 - pietroalbini:ci-fix-windows-python-path, r=Mark-Simulacrum
Rollup merge of #70116 - pietroalbini:ci-fix-windows-python-path, r=Mark-Simulacrum

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.

See https://github.com/rust-lang/rust/pull/70112#issuecomment-600760786 for the actual failure.

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