update checkout action

Author: hellt

.github/workflows/cicd.yml

@@ -13,7 +13,7 @@ jobs:
   docs-test:
     runs-on: ubuntu-20.04
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - run: docker run -v $(pwd):/docs --entrypoint mkdocs squidfunk/mkdocs-material:$MKDOCS_MATERIAL_VER build --clean --strict
       - name: htmltest
         run: |