automation: set PATH when building on Windows...
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`.
