downgrade cpp version by os

Author: szcf-weiya

.github/workflows/pkgdown.yaml

@@ -15,7 +15,7 @@ permissions: read-all
 
 jobs:
   pkgdown:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     # Only restrict concurrency for non-PR jobs
     concurrency:
       group: pkgdown-${{ github.event_name != 'pull_request' || github.run_id }}