Update the download action to version 6

See alert here: https://github.com/CRPropa/CRPropa3-data/security/dependabot/1

.github/workflows/upload.yml

@@ -29,7 +29,7 @@ jobs:
     # Create and Upload a file containing the current date to SCIEBO
     - name: Download artifact
       id: download-artifact
-      uses: dawidd6/action-download-artifact@v3
+      uses: dawidd6/action-download-artifact@v6
       with:
         # Optional, workflow file name or ID
         # If not specified, will be inferred from run_id (if run_id is specified), or will be the current workflow
@@ -91,4 +91,4 @@ jobs:
     #          The current download string is: ' + ${{ github.event.inputs.name }} + '.tar.gz'
     #      });
     #  env:
-    #    GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+    #    GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}