move files to respect the joss name "paper" only

Author: jalvesz

.github/workflows/draft-pdf.yml

@@ -17,10 +17,10 @@ jobs:
         uses: openjournals/openjournals-draft-action@master
         with:
           journal: joss
-          paper-path: joss/paper_sparse.md
+          paper-path: joss/sparse/paper.md
 
       - name: Upload PDF
         uses: actions/upload-artifact@v4
         with:
           name: paper
-          path: joss/paper.pdf
+          path: joss/sparse/paper.pdf