ci: notify only when failure

Author: wojtek-krysiak

.github/workflows/push.yml

@@ -91,7 +91,7 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK }}
-        if: always()
+        if: failure()
 
   publish:
     name: Publish