Fix checking out correct ref in build workflow

.github/workflows/build.yaml

@@ -20,7 +20,15 @@ jobs:
       changed: ${{ steps.grabchanged.outputs.changed }}
 
     steps:
+      - name: checkout local templates from prev workflow
+        if: "${{ github.event_name == 'workflow_run' }}"
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          ref: ${{ github.event.workflow_run.head_branch }}
+
       - name: checkout local templates
+        if: "${{ github.event_name != 'workflow_run' }}"
         uses: actions/checkout@v4
         with:
           fetch-depth: 0