add missing step for checking out code from tag

Author: nerrad

.github/workflows/wordpress-deploy.yml

@@ -7,6 +7,8 @@ jobs:
     name: New Release
     runs-on: ubuntu-latest
     steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
       - name: WordPress Plugin Deploy
         id: deploy
         uses: 10up/action-wordpress-plugin-deploy@stable