Similar error on the same build when the test was re-run in verbose mode:

0:10:55 load avg: 1.82 Re-running test_venv in verbose mode
test_deactivate_with_strict_bash_opts (test.test_venv.BasicTest) ... skipped 'not relevant on Windows'
test_defaults (test.test_venv.BasicTest) ... ok
test_executable (test.test_venv.BasicTest) ... ok
test_executable_symlinks (test.test_venv.BasicTest) ... skipped 'Needs symlinks'
test_isolation (test.test_venv.BasicTest) ... ok
test_multiprocessing (test.test_venv.BasicTest) ... ok
test_overwrite_existing (test.test_venv.BasicTest) ... ERROR
ERROR
test_prefixes (test.test_venv.BasicTest) ... ok
test_prompt (test.test_venv.BasicTest) ... ok
test_symlinking (test.test_venv.BasicTest) ... skipped 'Needs symlinks'
test_unicode_in_batch_file (test.test_venv.BasicTest) ... ok
test_unoverwritable_fails (test.test_venv.BasicTest) ... ok
test_upgrade (test.test_venv.BasicTest) ... ok
test_upgrade_dependencies (test.test_venv.BasicTest) ... ok
test_devnull (test.test_venv.EnsurePipTest) ... ok
test_explicit_no_pip (test.test_venv.EnsurePipTest) ... ok
test_no_pip_by_default (test.test_venv.EnsurePipTest) ... ok
test_with_pip (test.test_venv.EnsurePipTest) ... ok

======================================================================
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 223, 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 730, in rmtree
    return _rmtree_unsafe(path, onerror)
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\shutil.py", line 612, in _rmtree_unsafe
    onerror(os.rmdir, path, sys.exc_info())
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\shutil.py", line 610, in _rmtree_unsafe
    os.rmdir(path)
OSError: [WinError 145] The directory is not empty: 'C:\\Users\\Buildbot\\AppData\\Local\\Temp\\tmpvw7zok8k\\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 336, in _force_run
    return func(*args)
PermissionError: [WinError 5] Access is denied: 'C:\\Users\\Buildbot\\AppData\\Local\\Temp\\tmpvw7zok8k\\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 458, in rmtree
    _rmtree(path)
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\test\support\__init__.py", line 399, in _rmtree
    _waitfor(_rmtree_inner, path, waitall=True)
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\test\support\__init__.py", line 347, in _waitfor
    func(pathname)
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\test\support\__init__.py", line 395, 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 347, in _waitfor
    func(pathname)
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\test\support\__init__.py", line 398, 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 341, in _force_run
    os.chmod(path, stat.S_IRWXU)
PermissionError: [WinError 5] Access is denied: 'C:\\Users\\Buildbot\\AppData\\Local\\Temp\\tmpvw7zok8k\\Scripts\\activate.bat'

----------------------------------------------------------------------

Ran 18 tests in 45.669s

FAILED (errors=2, skipped=3)