Git object files are stored read-only in the filesystem. Trying to remove a
read-only file on windows will fail with access denied, so we have to make them
writeable before they can be removed.
Git might have autocrlf=true as a global or default setting, especially on
windows. That is not expected in the tests and can cause
+ warning: LF will be replaced by CRLF in d/b.
+ The file will have its original line endings in your working directory.
Explicitly setting it false will make the test pass in some setups - but still
not out of the box.
