Update GitHub Actions to latest versions to avoid deprecated command warnings

- Updated actions/checkout to v4
- Updated docker/setup-buildx-action to v3
- Updated docker/login-action to v3

Author: Marc Wolf

.github/workflows/ci.yml

@@ -14,13 +14,13 @@ jobs:
 
         steps:
             - name: Checkout repository
-              uses: actions/checkout@v2
+              uses: actions/checkout@v4
 
             - name: Set up Docker Buildx
-              uses: docker/setup-buildx-action@v1
+              uses: docker/setup-buildx-action@v3
 
             - name: Login to Docker Hub
-              uses: docker/login-action@v1
+              uses: docker/login-action@v3
               with:
                   username: ${{ secrets.DOCKERHUB_USERNAME }}
                   password: ${{ secrets.DOCKERHUB_TOKEN }}