Update checkout action to stable tag

Author: rtBot

.github/workflows/create.yml

@@ -7,7 +7,7 @@ jobs:
   tag:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2
       - name: WordPress Plugin Deploy
         uses: rtCamp/action-wordpress-org-plugin-deploy@master
         env: