ci: use unlimited node for previews (#115)

Author: vojtechsimetka

.github/workflows/check.yaml

@@ -66,9 +66,11 @@ jobs:
       - name: Create preview
         uses: ethersphere/beeload-action@v1
         with:
+          bee-url: https://unlimited.gateway.ethswarm.org
           preview: 'true'
           token: ${{ secrets.REPO_GHA_PAT }}
-
+          extra-params: '-H "${{ secrets.GATEWAY_AUTHORIZATION_HEADER }}"'
+          
       - name: Upload to testnet
         uses: ethersphere/beeload-action@v1
         with: