Remove Docker Hub auth (secrets not accessible from CI runners)

DOCKERHUB_USERNAME/DOCKERHUB_TOKEN secrets are not accessible from
the self-hosted runners. Remove credentials blocks and login steps
to avoid template validation failures. Docker Hub pulls will use
anonymous access.

Refs: CAR-77

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.github/workflows/ci.yml

@@ -68,12 +68,6 @@ jobs:
             type=sha,prefix=sha-
             type=raw,value=latest,enable=${{ github.ref == 'refs/heads/main' }}
 
-      - name: Log in to Docker Hub
-        uses: docker/login-action@v3
-        with:
-          username: ${{ secrets.DOCKERHUB_USERNAME }}
-          password: ${{ secrets.DOCKERHUB_TOKEN }}
-
       - name: Build and push Docker image
         uses: docker/build-push-action@v6
         with: