GitHub Actions: pull LFS objects on checkout (lfs: true)

Without this, the build copies the 134-byte LFS pointer text instead
of the actual binary content for files in LFS — which means LFS-stored
PDFs end up published as broken pointer-only files.

Author: rhiju

.github/workflows/pages.yml

@@ -19,6 +19,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          lfs: true
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: "3.3"