Update pkgdown.yaml

Back to ubuntu

Author: robjhyndman

Diff for: .github/workflows/pkgdown.yaml

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