Skip the uploadtwice02 test on non-Windows systems

[mapix]

Since os.unlink() is non-blocking on Linux and macOS, uploadtwice02 may hinder contributions from developers on non-Windows platforms.

[fohrloop]

Would it make more sense to fix the test instead of skipping it? There must be a reason the test_uploadtwice02_upload_a_file_twice_with_error exists in the first place. I did not understand the os.unlink() reference. Did you mean that reserve_file_for_while does not reserve the file on linux? Or something else?

And I fully support making contributions easier. As I just commented on the another PR, I feel that setting up the dev env is a bit difficult. If we can make the instructions easier to follow, that would be great!

Edit: I see you've also mentioned this issue on your previous PR ( #130 )

[fohrloop]

Hi @mapix , I took another look. Now I see why there was such a test in the first place. I did some changes and pushed them to a separate PR #140. Closing this one.