Fix test suite clean up (Neon)

[twangboy]

What does this PR do?

Skips PermissionError when trying to delete the test directory after a test run. Git maintains open file handles on git index files causing the following stacktrace when trying to clean up:

:1183][ERROR   ] Failed to remove directory: C:\Users\ADMINI~1\AppData\Local\Temp\salt-tests-tmpdir
15:52:35         Traceback (most recent call last):
15:52:35           File "c:\users\admini~1\appdata\local\temp\kitchen\testing\.nox\runtests-parametrized-3-coverage-true-crypto-none-transport-zeromq\lib\shutil.py", line 387, in _rmtree_unsafe
15:52:35             os.unlink(fullname)
15:52:35         PermissionError: [WinError 5] Access is denied: 'C:\\Users\\ADMINI~1\\AppData\\Local\\Temp\\salt-tests-tmpdir\\tmp216ldwzw\\gitfs\\709b529e4651ea331ec097c44268cba9\\.git\\objects\\pack\\pack-1a59b5f484045d2294d42df3e17258d44443fa5d.idx'

What issues does this PR fix or reference?

gitpython-developers/GitPython#546

Commits signed with GPG?

Yes

[dwoz]

OSError will already be caught by the general Exception catching.