Installing packages with non-privileged users on Windows, failed with PermissionError

[catPill]

Environment

• pip version: 20.0.2
• Python version: 3.8.2
• OS: Windows 10

Description

Installing packages with non-privileged users on Windows, failed with PermissionError.

Expected behavior

Should detect site-packages folder is not writable, try install to user appdata folder instead.

How to Reproduce

Run pip install pandas with non-privileged user on windows.

Output

ERROR: Exception:
Traceback (most recent call last):
  File "c:\program files (x86)\python38-32\lib\site-packages\pip\_internal\cli\base_command.py", line 186, in _main
    status = self.run(options, args)
  File "c:\program files (x86)\python38-32\lib\site-packages\pip\_internal\commands\install.py", line 253, in run
    options.use_user_site = decide_user_install(
  File "c:\program files (x86)\python38-32\lib\site-packages\pip\_internal\commands\install.py", line 604, in decide_user_install
    if site_packages_writable(root=root_path, isolated=isolated_mode):
  File "c:\program files (x86)\python38-32\lib\site-packages\pip\_internal\commands\install.py", line 548, in site_packages_writable
    return all(
  File "c:\program files (x86)\python38-32\lib\site-packages\pip\_internal\commands\install.py", line 549, in <genexpr>
    test_writable_dir(d) for d in set(get_lib_location_guesses(**kwargs))
  File "c:\program files (x86)\python38-32\lib\site-packages\pip\_internal\utils\filesystem.py", line 140, in test_writable_dir
    return _test_writable_dir_win(path)
  File "c:\program files (x86)\python38-32\lib\site-packages\pip\_internal\utils\filesystem.py", line 153, in _test_writable_dir_win
    fd = os.open(file, os.O_RDWR | os.O_CREAT | os.O_EXCL)
PermissionError: [Errno 13] Permission denied: 'c:\\program files (x86)\\python38-32\\Lib\\site-packages\\accesstest_deleteme_fishfingers_custard_m59lch'

With pdb I notice os.open raise a OSError which errno is errno.EACCES.

[SanketDG]

Related to #1668