Update actions/upload-artifact to v4

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

Author: sim642

.github/workflows/build.yml

@@ -40,7 +40,7 @@ jobs:
         run: vsce package
 
       - name: Upload plugin artifact
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: gobpie-plugin
           path: ./vscode/gobpie-*.vsix