Use USERPROFILE in expanduser test
Use USERPROFILE in expanduser test

In Python 3.8, expanduser on Windows no longer respects HOME, per
https://bugs.python.org/issue36264.

sbidoul/pip,sbidoul/pip,pypa/pip,pfmoore/pip,pradyunsg/pip,pradyunsg/pip,pypa/pip,pfmoore/pip