CI: upgrade upload-artifact, download-artifact

Following deprecation notice at https://github.blog/changelog/2024-04-16-deprecation-notice-v3-of-the-artifact-actions/

.github/workflows/slycot-build-and-test.yml

@@ -126,7 +126,7 @@ jobs:
           mkdir -p ${wheeldir}
           cp ./slycot*.whl ${wheeldir}/
       - name: Save wheel
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: slycot-wheels
           path: slycot-wheels
@@ -176,7 +176,7 @@ jobs:
           done
           python -m conda_index ./slycot-conda-pkgs
       - name: Save to local conda pkg channel
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: slycot-conda-pkgs
           path: slycot-conda-pkgs
@@ -192,7 +192,7 @@ jobs:
       - name: Checkout Slycot
         uses: actions/checkout@v3
       - name: Download wheels (if any)
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: slycot-wheels
           path: slycot-wheels
@@ -210,7 +210,7 @@ jobs:
       - name: Checkout Slycot
         uses: actions/checkout@v3
       - name: Download conda packages
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: slycot-conda-pkgs
           path: slycot-conda-pkgs
@@ -272,7 +272,7 @@ jobs:
               exit 1 ;;
           esac
       - name: Download wheels
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: slycot-wheels
           path: slycot-wheels
@@ -331,7 +331,7 @@ jobs:
           channel-priority: strict
           auto-activate-base: false
       - name: Download conda packages
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: slycot-conda-pkgs
           path: slycot-conda-pkgs