build(deps): bump actions/download-artifact from 4 to 8 in launcher-appimage

The job downloads one artifact by name into a path, so the v5 single-ID path change does not apply. Every other workflow already uses v8. Applies mudler/LocalAI#12719.

Assisted-by: Claude:claude-sonnet-5-5 gh git
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

.github/workflows/launcher-appimage.yaml

@@ -60,7 +60,7 @@ jobs:
       contents: write
     steps:
       # Download only: never execute repository code with the write token.
-      - uses: actions/download-artifact@v4
+      - uses: actions/download-artifact@v8
         with:
           name: launcher-appimage-x86_64
           path: dist