Fix staging branch name in workflow

The workflow create the branch staging, so we cannot have exactly `staging`

Author: Zwyx

.github/workflows/build-website.yml

@@ -8,7 +8,7 @@ on:
     tags:
       - "v[0-9]+.[0-9]+.[0-9]+"
     branches:
-      - "staging**"
+      - "staging/**"
   workflow_dispatch:
 
 permissions: