I marked bpo-38983 as a duplicate of this issue. It's the same error in the same function (clear_directory()). Copy of the first message:

Failure on AMD64 Windows7 SP1 3.x:
https://buildbot.python.org/all/#builders/81/builds/16

======================================================================
ERROR: test_overwrite_existing (test.test_venv.BasicTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\test\test_venv.py", line 225, in test_overwrite_existing
    builder.create(self.env_dir)
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\venv\__init__.py", line 65, in create
    context = self.ensure_directories(env_dir)
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\venv\__init__.py", line 108, in ensure_directories
    self.clear_directory(env_dir)
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\venv\__init__.py", line 91, in clear_directory
    shutil.rmtree(fn)
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\shutil.py", line 731, in rmtree
    return _rmtree_unsafe(path, onerror)
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\shutil.py", line 613, in _rmtree_unsafe
    onerror(os.rmdir, path, sys.exc_info())
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\shutil.py", line 611, in _rmtree_unsafe
    os.rmdir(path)
OSError: [WinError 145] The directory is not empty: 'C:\\Users\\Buildbot\\AppData\\Local\\Temp\\tmp9y0m6j7z\\Scripts'

======================================================================
ERROR: test_overwrite_existing (test.test_venv.BasicTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\test\support\__init__.py", line 380, in _force_run
    return func(*args)
PermissionError: [WinError 5] Access is denied: 'C:\\Users\\Buildbot\\AppData\\Local\\Temp\\tmp9y0m6j7z\\Scripts\\activate.bat'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\test\test_venv.py", line 71, in tearDown
    rmtree(self.env_dir)
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\test\support\__init__.py", line 502, in rmtree
    _rmtree(path)
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\test\support\__init__.py", line 443, in _rmtree
    _waitfor(_rmtree_inner, path, waitall=True)
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\test\support\__init__.py", line 391, in _waitfor
    func(pathname)
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\test\support\__init__.py", line 439, in _rmtree_inner
    _waitfor(_rmtree_inner, fullname, waitall=True)
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\test\support\__init__.py", line 391, in _waitfor
    func(pathname)
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\test\support\__init__.py", line 442, in _rmtree_inner
    _force_run(fullname, os.unlink, fullname)
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\test\support\__init__.py", line 385, in _force_run
    os.chmod(path, stat.S_IRWXU)
PermissionError: [WinError 5] Access is denied: 'C:\\Users\\Buildbot\\AppData\\Local\\Temp\\tmp9y0m6j7z\\Scripts\\activate.bat