chore(deps): update actions/checkout action to v4

Author: renovate[bot]

.github/workflows/docker.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
       - name: Build an image from Dockerfile
         run: docker build -t trivy-explorer .
       - name: Run Trivy vulnerability scanner