chore: Update actions/checkout action to v4

Author: renovate[bot]

.github/workflows/publish.yaml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     container: python:3.8
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Install system dependencies.
         run: apt-get update && apt-get install -y rsync
       - name: Install the site generator.

.github/workflows/test.yaml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     container: python:3.8
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Install the site-generator
         run: pip install -r requirements.txt
       - name: Build the site.