[BUG] Pip package manager tests fail on Windows

[zachcran]

Describe the bug
The pip testing (tests/cmake/package_managers/pip/test_pip.cmake) assumes that the Python venv is set up on Linux, with the Linux venv paths hard-coded. This causes the pip tests to fail on Windows.

Expected behavior
The tests should be platform agnostic, or at least support Windows, Mac, and Linux, and pass on all platforms.

Additional context
On Windows, the <venv>/bin/ directory is replaced with <venv>/Scripts/ (case insensitive). Additionally, python3 is no longer an executable in <venv>/Scripts/, with only python.exe provided (will respond to just python). Oddly, pip.exe, pip3.exe, and pip3.<minor_version>.exe are still all there.