poetry: `poetry self update --preview` leads to `[WinError 5] Access is denied: 'py3.7\\msgpack\\_cmsgpack.cp37-win_amd64.pyd'`

• I am on the latest Poetry version.
• I have searched the issues of this repo and believe that this is not a duplicate.
• If an exception occurs when executing a command, I executed it again in debug mode (-vvv option).

• OS version and name: Windows 10 pro, version 1909
• Poetry version: 1.0.9
• Link of a Gist with the contents of your pyproject.toml file: no project specific probelm

Issue

I use powershell and pyenv on windows with python 3.7. Python 3.7.5 is the newest version according to pyenv install -l Updating to the latest preview does not work as expected, I assumed poetry self update --preview would work. But see the log below, I can reproduce it every time with the same error. Installing/using poetry 1.0.9 works without issues. I guess it is similar to #1032 as shutil.py is involved in both problems, but the error is different.

Steps to reproduce

1. install poetry with (Invoke-WebRequest -Uri https://raw.githubusercontent.com/python-poetry/poetry/master/get-poetry.py -UseBasicParsing).Content | python
2. try to update with poetry self update --preview

Afterwards the poetry installation is corrupted and does not work anymore

Workaround powershell command

1. delete the .poetry folder manually (located in user home directory)
2. (Invoke-WebRequest -Uri https://raw.githubusercontent.com/python-poetry/poetry/master/get-poetry.py -UseBasicParsing).Content | python - --preview

Log that shows error

PS C:\Users\jahna> (Invoke-WebRequest -Uri https://raw.githubusercontent.com/python-poetry/poetry/master/get-poetry.py -UseBasicParsing).Content | python
Retrieving Poetry metadata

# Welcome to Poetry!

This will download and install the latest version of Poetry,
a dependency and package manager for Python.

It will add the `poetry` command to Poetry's bin directory, located at:

%USERPROFILE%\.poetry\bin

This path will then be added to your `PATH` environment variable by
modifying the `HKEY_CURRENT_USER/Environment/PATH` registry key.

You can uninstall at any time by executing this script with the --uninstall option,
and these changes will be reverted.

Installing version: 1.0.9
  - Downloading poetry-1.0.9-win32.tar.gz (10.72MB)

Poetry (1.0.9) is installed now. Great!

To get started you need Poetry's bin directory (%USERPROFILE%\.poetry\bin) in your `PATH`
environment variable. Future applications will automatically have the
correct environment, but you may need to restart your current shell.

PS C:\Users\jahna> poetry self update --preview -vvv
Updating to 1.1.0a3

[PermissionError]
[WinError 5] Access is denied: 'C:\\Users\\jahna\\.poetry\\lib\\poetry\\_vendor\\py3.7\\msgpack\\_cmsgpack.cp37-win_amd64.pyd'

Traceback (most recent call last):
  File "C:\Users\jahna\.poetry\lib\poetry\_vendor\py3.7\clikit\console_application.py", line 131, in run
  File "C:\Users\jahna\.poetry\lib\poetry\_vendor\py3.7\clikit\api\command\command.py", line 120, in handle
  File "C:\Users\jahna\.poetry\lib\poetry\_vendor\py3.7\clikit\api\command\command.py", line 171, in _do_handle
  File "C:\Users\jahna\.poetry\lib\poetry\_vendor\py3.7\cleo\commands\command.py", line 92, in wrap_handle
  File "C:\Users\jahna\.poetry\lib\poetry\console\commands\self\update.py", line 134, in handle
  File "C:\Users\jahna\.poetry\lib\poetry\console\commands\self\update.py", line 146, in update
  File "C:\Users\jahna\.pyenv\pyenv-win\versions\3.7.5-amd64\lib\shutil.py", line 516, in rmtree
    return _rmtree_unsafe(path, onerror)
  File "C:\Users\jahna\.pyenv\pyenv-win\versions\3.7.5-amd64\lib\shutil.py", line 395, in _rmtree_unsafe
    _rmtree_unsafe(fullname, onerror)
  File "C:\Users\jahna\.pyenv\pyenv-win\versions\3.7.5-amd64\lib\shutil.py", line 395, in _rmtree_unsafe
    _rmtree_unsafe(fullname, onerror)
  File "C:\Users\jahna\.pyenv\pyenv-win\versions\3.7.5-amd64\lib\shutil.py", line 395, in _rmtree_unsafe
    _rmtree_unsafe(fullname, onerror)
  [Previous line repeated 1 more time]
  File "C:\Users\jahna\.pyenv\pyenv-win\versions\3.7.5-amd64\lib\shutil.py", line 400, in _rmtree_unsafe
    onerror(os.unlink, fullname, sys.exc_info())
  File "C:\Users\jahna\.pyenv\pyenv-win\versions\3.7.5-amd64\lib\shutil.py", line 398, in _rmtree_unsafe
    os.unlink(fullname)
PermissionError: [WinError 5] Access is denied: 'C:\\Users\\jahna\\.poetry\\lib\\poetry\\_vendor\\py3.7\\msgpack\\_cmsgpack.cp37-win_amd64.pyd'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\jahna\.poetry\bin\poetry", line 18, in <module>
    main()
  File "C:\Users\jahna\.poetry\lib\poetry\console\__init__.py", line 5, in main
  File "C:\Users\jahna\.poetry\lib\poetry\_vendor\py3.7\clikit\console_application.py", line 139, in run
  File "C:\Users\jahna\.poetry\lib\poetry\_vendor\py3.7\clikit\ui\components\exception_trace.py", line 58, in render
  File "C:\Users\jahna\.poetry\lib\poetry\_vendor\py3.7\clikit\ui\components\exception_trace.py", line 63, in _render_traceback
  File "C:\Users\jahna\.poetry\lib\poetry\_vendor\py3.7\clikit\ui\components\exception_trace.py", line 75, in _format_traceback_frame
TypeError: 'NoneType' object is not subscriptable