fix(ci): remove unnecessary Docker Hub login step

The build-and-push job had an unconditional Docker Hub login step that
was failing because DOCKERHUB_USERNAME and DOCKERHUB_TOKEN secrets are
not provisioned. Since we push images to GHCR (not Docker Hub), this
step is not needed.

Closes cartsnitch/infra#5

Co-authored-by: deploy-debbie[bot] <268472978+deploy-debbie[bot]@users.noreply.github.com>
Co-authored-by: Paperclip <noreply@paperclip.ing>

.github/workflows/ci.yml

@@ -51,12 +51,6 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - name: Log in to Docker Hub
-        uses: docker/login-action@v3
-        with:
-          username: ${{ secrets.DOCKERHUB_USERNAME }}
-          password: ${{ secrets.DOCKERHUB_TOKEN }}
-
       - name: Log in to GHCR
         if: github.event_name == 'push' && github.ref == 'refs/heads/main'
         uses: docker/login-action@v3