chore(ci): use correct git ref for mcp-publish (#8589)

Author: Lukas742

.github/workflows/publish-mcp-registry.yml

@@ -22,6 +22,8 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          ref: main
 
       - name: Install mcp-publisher
         run: |