Bump checkout to v6 and upload-artifact to v7

The v4 releases run on Node.js 20, which GitHub Actions is
deprecating; the new majors ship on Node.js 24.

Author: ad-si

.github/workflows/build-artifacts.yml

@@ -22,7 +22,7 @@ jobs:
           - wolfram-language
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Install Nix
         uses: cachix/install-nix-action@v26
@@ -57,7 +57,7 @@ jobs:
           cp ${{ matrix.language }}/cards.pdf  cards-${{ matrix.language }}.pdf
 
       - name: Upload artifacts to workflow run
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v7
         with:
           name: cards-${{ matrix.language }}
           path: |