Maintenance: Improve test coverage on Windows

[ddneilson]

Description

The _locate_for_other_user function has poor test coverage when running tests without impersonation, and is missing coverage of exceptional cases when running with impersonation.

It has been marked as nocover for now, but the test coverage needs to be improved.

Solution

Write some tests for locate_windows_executable that will exercise the untested sections of the _locate_for_other_user function.