Add build step

.github/workflows/deploy_mkdocs.yml

@@ -20,8 +20,11 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         pip install -r requirements.txt
+    
+    - name: Build MkDocs site
+      run: mkdocs build
 
-    - name: Build and deploy
+    - name: Deploy MkDocs site
       uses: peaceiris/actions-gh-pages@v3
       with:
         github_token: ${{ secrets.GITHUB_TOKEN }}