CI: update draft-pdf.yml actions version

cf. https://github.blog/changelog/2024-02-13-deprecation-notice-v1-and-v2-of-the-artifact-actions/

.github/workflows/draft-pdf.yml

@@ -14,7 +14,7 @@ jobs:
           # This should be the path to the paper within your repo.
           paper-path: paper.md
       - name: Upload
-        uses: actions/upload-artifact@v1
+        uses: actions/upload-artifact@v4
         with:
           name: paper
           # This is the output path where Pandoc will write the compiled