Update actions/checkout action to v4

Author: renovate[bot]

.github/workflows/docker-publish.yml

@@ -24,7 +24,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
       - name: Run tests
         run: |
@@ -44,7 +44,7 @@ jobs:
     if: github.event_name == 'push'
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
       - name: Build image
         run: docker build . --file Dockerfile --tag $IMAGE_NAME