action/compile: Update checkout to use PR head

Signed-off-by: Audun Korneliussen <[email protected]>

Author: nordic-auko

.github/workflows/compile-samples.yml

@@ -33,6 +33,8 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v4
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
 
       - name: Parse NCS revision
         id: parse_revision