Use config._tmp_path_factory instead of config._tmpdirhandler
Use config._tmp_path_factory instead of config._tmpdirhandler

Both are private, and shouldn't be used, but not sure how to fix it
currently. But `_tmpdirhandler` will be relegated to the legacypath
plugin so should extra not be used.

pytest-dev/pytest-xdist,nicoddemus/pytest-xdist