Add pr head commit for validation

.github/workflows/checks.yml

@@ -9,8 +9,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
         with:
-          repository: ${{ github.repository }}
+          ref: ${{ github.event.pull_request.head.sha }}
-          ref: ${{ github.head_ref }}
           fetch-depth: 0
       - name: Installing dependencies
         uses: borales/actions-yarn@v2.0.0