ci: do not post updates about enterprise releases to emqx.io

.github/workflows/release.yaml

@@ -69,9 +69,9 @@ jobs:
         with:
           asset_paths: '["packages/*"]'
       - name: update to emqx.io
-        if: github.event_name == 'release' || inputs.publish_release_artefacts
+        if: startsWith(github.ref_name, 'v') && (github.event_name == 'release' || inputs.publish_release_artefacts)
         run: |
-          set -e -x -u
+          set -eux
           curl -w %{http_code} \
                --insecure \
                -H "Content-Type: application/json" \