My favorite palindrome (#7455)

* My favorite palindrome

* updating DIRECTORY.md

* Update is_palindrome.py

* Update is_palindrome.py

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update strings/is_palindrome.py

Co-authored-by: Caeden Perelli-Harris <caedenperelliharris@gmail.com>

* Update is_palindrome.py

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Caeden Perelli-Harris <caedenperelliharris@gmail.com>