fix: use workflow_run event context

.github/workflows/progress.yml

@@ -16,7 +16,7 @@ jobs:
         uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
         with:
           fetch-depth: 0
-          ref: ${{ github.event.pull_request.head.ref }}
+          ref: ${{ github.event.workflow_run.head_branch }}
 
       - name: Update README progress
         run: |