ci: Update upload-artifact and download-artifact (#68)

The older versions are deprecated and will stop working next month.

.github/workflows/release.yaml

@@ -128,7 +128,7 @@ jobs:
           cp shaka-*/windows/*.nupkg staging/
 
       - name: Upload packages
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: windows-packages
           path: staging/
@@ -141,7 +141,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Download packages
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: windows-packages