Bump actions/checkout from 3 to 4 (#22)

Author: dependabot[bot]

.github/workflows/DocPreviewCleanup.yml

@@ -11,7 +11,7 @@ jobs:
       contents: write
     steps:
       - name: Checkout gh-pages branch
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           ref: gh-pages
       - name: Delete preview and history + push changes