Fix paper build by updating upload-artifact action

Update actions/upload-artifact from deprecated v1 to v4 to fix
paper build failures.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: orionarcher

.github/workflows/draft-pdf.yml

@@ -14,7 +14,7 @@ jobs:
           # This should be the path to the paper within your repo.
           paper-path: joss_paper/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