Update actions/checkout action to v4

Author: renovate[bot]

.github/workflows/publish.yaml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout main
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
       - name: Deploy docs
         uses: mhausenblas/mkdocs-deploy-gh-pages@master
         env: