tooling: build gfm for winter 2025/26 (_w25 branch)

Author: cagix

.github/workflows/pdf.yaml

@@ -24,6 +24,6 @@ jobs:
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: _pdf
-          publish_branch: _pdf
+          publish_branch: _w25    ## TODO (semester branch)
           force_orphan: true
           commit_message: ${{ github.event.head_commit.message }}