automation: set PATH when building on Windows Sometime in the 6.2 release cycle the Windows building automation broke. Building the wheel and even PyOxidizer based installers now fails with: ``` Exception: PowerShell execution failed: error: subprocess-exited-with-error Getting requirements to build wheel did not run successfully. exit code: 1 [1 lines of output] Unable to find a working hg binary to extract the version from the repository tags [end of output] note: This error originates from a subprocess, and is likely not a problem with pip. ``` I have a hunch this is a regression from upgrading pip in 1c00777702da, but I haven't verified this. It may not be, as PyOxidizer has its own bundled Python/pip. So maybe it is something in `setup.py`.