Dulwich: Symlink write-through in checkout(paths=[]) via raw os.open bypasses all symlink protections

Summary Dulwich's porcelain.checkoutpaths=... code path writes files using raw os.openfilepath, OWRONLY|OCREAT|OTRUNC, mode followed by f.writeobj.data. This code path does NOT call buildfilefromblob at all, completely bypassing any symlink protections including the unreleased d09f8af fix. os.ope...