Update GitHub Actions to use upload-artifact@v4

Author: bvdmitri

.github/workflows/CI.yml

@@ -35,7 +35,7 @@ jobs:
           journal: joss
           # This should be the path to the paper within your repo.
           paper-path: paper/paper.md
-      - uses: actions/upload-artifact@v1
+      - uses: actions/upload-artifact@v4
         with:
           name: paper
           # This is the output path where Pandoc will write the compiled
@@ -71,7 +71,7 @@ jobs:
         env:
           CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
       - name: Archive test artifacts
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         with:
           name: test-output
           path: test/_output