Remove uneccessary checkout and avoid race condition

Author: AndyTitu

.github/workflows/validate.yml

@@ -79,10 +79,7 @@ jobs:
     - name: Fork based /ok-to-test checkout
       uses: actions/checkout@v4
       with:
-        ref: 'refs/pull/${{ github.event.client_payload.pull_request.number }}/merge'
-
-    
-    - uses: actions/checkout@v4
+        ref: ${{ github.event.client_payload.pull_request.head.sha }}
 
     - name: Set up Python
       uses: actions/setup-python@v4