fix(ci): litmus test with current upload-artifact

The older versions were deprecated earlier this year:
https://github.blog/changelog/2024-02-13-deprecation-notice-v1-and-v2-of-the-artifact-actions/

Signed-off-by: Max <max@nextcloud.com>

.github/workflows/litmus.yml

@@ -109,15 +109,15 @@ jobs:
         run: cat data/nextcloud.log
 
       - name: Upload litmus logs
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         if: failure()
         with:
           name: Upload litmus log
           path: /tmp/litmus/litmus-0.13/debug.log
           retention-days: 5
 
       - name: Upload nextcloud logs
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         if: failure()
         with:
           name: Upload nextcloud log