Updated circular_linked_list (#2483)

* Updated circular_linked_list

* fixup! Format Python code with psf/black push

* Update data_structures/linked_list/circular_linked_list.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* updating DIRECTORY.md

* delete print_list()

* test is_empty()

* test is_empty return False

* fixup! Format Python code with psf/black push

* fixed indentation

* fixup! Format Python code with psf/black push

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Co-authored-by: Christian Clauss <cclauss@me.com>