An attempt to fix the failing builds

.github/workflows/php.yml

@@ -11,6 +11,9 @@ jobs:
     steps:
     - name: Check out repository
       uses: actions/checkout@v2
+      with:
+        ref: ${{ github.head_ref }}
+        repository: ${{ github.event.pull_request.head.repo.full_name }}
 
     - name: Set up PHP
       uses: shivammathur/setup-php@v2