Update build.yml

.github/workflows/build.yml

@@ -26,7 +26,7 @@ jobs:
         git init 
         git config --global user.name "github-actions[bot]"
         git config --global user.email "${{ secrets.DRAGONOS_EMAIL }}"
-        git checkout gh-pages
+        git branch gh-pages && git checkout gh-pages
         git add .
         git commit -m "deploy"
         git push -f [email protected]:DragonOS-Community/OS_lab_tutorial.git gh-pages