GitHubCI: update upload-artifact from v3 to v4

Otherwise it fails with:
```
Error: This request has been automatically failed because it uses a deprecated version of `actions/upload-artifact: v3`. Learn more: https://github.blog/changelog/2024-04-16-deprecation-notice-v3-of-the-artifact-actions/
```

Author: knocte

.github/workflows/CI.yml

@@ -693,7 +693,7 @@ jobs:
     - name: Test snap
       run: gwallet --version
 
-    - uses: actions/upload-artifact@v3
+    - uses: actions/upload-artifact@v4
       name: Upload snap package as artifact
       with:
         name: snap