Update check_pr.yml

.github/workflows/check_pr.yml

@@ -15,6 +15,9 @@ jobs:
     steps:
       - name: Checkout source code
         uses: actions/checkout@v2
+        with:
+         ref: ${{ github.event.pull_request.head.sha }}
+
       - name: json-yaml-validate
         id: json-yaml-validate
         uses: GrantBirki/json-yaml-validate@v2.4.0