tests: mock test_conf_file_not_found filesystem access
tests: mock test_conf_file_not_found filesystem access

Fix #3699

rtfd/readthedocs.org,safwanrahman/readthedocs.org,davidfischer/readthedocs.org,rtfd/readthedocs.org,safwanrahman/readthedocs.org,rtfd/readthedocs.org,safwanrahman/readthedocs.org,rtfd/readthedocs.org,davidfischer/readthedocs.org,davidfischer/readthedocs.org,safwanrahman/readthedocs.org,davidfischer/readthedocs.org