feat: update docs workflow to pin Action

Author: GeekMasher

.github/workflows/docs.yml

@@ -27,7 +27,7 @@ jobs:
           pipenv run docs
 
       - name: Publish
-        uses: peaceiris/actions-gh-pages@v3
+        uses: peaceiris/actions-gh-pages@373f7f263a76c20808c831209c920827a82a2847  # v3.9.3
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: ./public