Update actions/checkout action to v4

Author: renovate[bot]

.github/workflows/build.yml

@@ -10,7 +10,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - run: |
         mkdir .jekyll-cache _site
         docker-compose up --exit-code-from jekyll

.github/workflows/deploy.yml

@@ -8,7 +8,7 @@ jobs:
   deploy:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Install dependencies
       run: sudo apt-get -q update && sudo apt-get install -y --no-install-recommends brotli zopfli
     - name: Build