fix: Ensure PR preview cleanup checks out repo on close (#396)

Author: elibosley

.github/workflows/pr.yml

@@ -61,14 +61,22 @@ jobs:
       contents: write
       pull-requests: write
     steps:
-      - name: Checkout
+      - name: Checkout PR branch
         uses: actions/checkout@v5
         if: ${{ github.event.action != 'closed' }}
         with:
           repository: ${{ github.event.pull_request.head.repo.full_name }}
           ref: ${{ github.event.pull_request.head.sha }}
           persist-credentials: false
 
+      - name: Checkout base branch
+        uses: actions/checkout@v5
+        if: ${{ github.event.action == 'closed' }}
+        with:
+          repository: ${{ github.event.pull_request.base.repo.full_name }}
+          ref: ${{ github.event.pull_request.base.ref }}
+          persist-credentials: false
+
       - name: Setup Node.js
         uses: actions/setup-node@v6
         if: ${{ github.event.action != 'closed' }}