Remove ref from checkout step

.github/workflows/prettier.yml

@@ -13,7 +13,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
         with: 
-          ref: ${{ github.head_ref }}
+          # ref: ${{ github.head_ref }}
           fetch-depth: 0
       - name: Use Node.js
         uses: actions/setup-node@v2