switch to newer github actions

Author: jgieseler

.github/workflows/main.yml

@@ -13,7 +13,7 @@ jobs:
                                # using "pandoc/latex" because of dependencies
                                # used in the specific "build.sh"
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Pushes to another repository
         uses: cpina/github-action-push-to-another-repository@main
         env: