docs: use master for mkdocs-deploy-gh-pages

Author: ken-matsui

.github/workflows/docs.yml

@@ -12,7 +12,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Deploy docs
-        uses: mhausenblas/mkdocs-deploy-gh-pages@nomaterial
+        uses: mhausenblas/mkdocs-deploy-gh-pages@master
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           CUSTOM_DOMAIN: docs.poac.dev