github action: update checkout to latest v4

Author: Mcouedel

.github/workflows/ci.yml

@@ -5,7 +5,7 @@ jobs:
     name: Build Jekyll
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: ruby/setup-ruby@v1
         with:
          ruby-version: '3.3'