Update check.yaml

change ref in an attempt to correct checkout problems with forked repositories

.github/workflows/check.yaml

@@ -12,7 +12,7 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v4
         with:
-          ref: ${{ github.head_ref }}
+          ref: ${{ github.event.pull_request.head.ref }}
 
       - name: Install packages
         run: npm install exiftool-vendored@26