CLDR-17803 docs/site: fix merge to main

- only update PR if there's a PR
- Merge to main should update the production deployment

.github/workflows/site.yml

@@ -39,15 +39,27 @@ jobs:
     - name: Pre-install Wrangler
       run: npm i -g [email protected]
       # see https://github.com/cloudflare/wrangler-action/issues/286
+    - name: Set the environment
+      id: chooser
+      run: |
+        echo ${{ github.event_name }} ${{ github.ref }} ;
+        if [[ "${{ github.event_name }}" == 'push' && "${{ github.ref }}" == 'refs/heads/main' ]]; then
+            echo cenv=production >> $GITHUB_OUTPUT
+            echo prod
+        else
+            echo cenv=preview >> $GITHUB_OUTPUT
+            echo preview
+        fi
     - name: Deploy cldr.pages.dev
       id: deploy
       uses: cloudflare/wrangler-action@v3
       with:
         apiToken: ${{ secrets.CLOUDFLARE_API_TOKEN }}
         accountId: ${{ secrets.CLOUDFLARE_ACCOUNT_ID }}
-        command: pages deploy ./_site --project-name=cldr
+        command: pages deploy ./_site --project-name=cldr --branch ${{ steps.chooser.outputs.cenv }}
     - name: Add deploy comment to PR
       uses: actions/github-script@v7
+      if: github.event_name == 'pull_request'
       with:
         script: |
           github.rest.issues.createComment({