chore: fix workflow (#1112)

just a test for running on main branch. related to reactjs/react.dev#5801. maybe revert at last.

Author: awxiaoxian2020

.github/workflows/analyze.yml

@@ -51,7 +51,7 @@ jobs:
         if: success() && github.event.number
         with:
           workflow: analyze.yml
-          branch: ${{ github.event.pull_request.base.ref }}
+          branch: ${{ github.event.pull_request.base.ref || 'main' }} 
           name: bundle_analysis.json
           path: .next/analyze/base/bundle