fix(ci): improve pr number handling for artifact upload

Author: SonyLeo

.github/workflows/pr-ci-build.yml

@@ -46,7 +46,7 @@ jobs:
         run: pnpm -F docs build
 
       - name: Save PR number
-        run: echo "${{ github.event.number }}" > pr_number.txt
+        run: echo "${{ github.event.pull_request.number }}" > pr_number.txt
 
       - name: Upload build artifacts
         uses: actions/upload-artifact@v4