Checkout pull request branch

Author: kevinbackhouse

.github/workflows/smoketest.yaml

@@ -31,7 +31,9 @@ jobs:
           python-version: '3.11'
 
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v5
+        with:
+          ref: ${{ github.head_ref }}
 
       - name: Setup Python venv
         run: |