This commit updates the `.github/workflows/mkdocs.yml` file to use the latest versions of the `actions/checkout` and `actions/setup-python` actions.
Key changes:
- Upgraded `actions/checkout` from `v2` to `v4`.
- Upgraded `actions/setup-python` from `v2` to `v5`.
- Pinned the Python version to `'3.11'`.
- Added `permissions: contents: write` to the `deploy` job to ensure the workflow has the necessary permissions to publish to GitHub Pages.
