upgraded actions/upload-artifact from v1 to v4

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

Author: Savalle Renaud

.github/workflows/build.yml

@@ -39,7 +39,7 @@ jobs:
         test -f ${{ env.doc_name }}.bbl
         
     - name: Keep the PDF artefact 
-      uses: actions/upload-artifact@v1
+      uses: actions/upload-artifact@v4
       with:
         name: PDF Preview
         path: ${{ env.doc_name }}.pdf