fix: keep backup OTA artifact alongside release assets

.gitea/workflows/ota-build.yml

@@ -49,6 +49,13 @@ jobs:
           fi
           find dist/ota -maxdepth 1 -type f | sort
 
+      - name: Upload backup OTA artifact ZIP
+        uses: actions/upload-artifact@v3
+        with:
+          name: ota-files
+          path: dist/ota/*
+          if-no-files-found: error
+
       - name: Publish raw OTA files to rolling release
         env:
           GITEA_TOKEN: ${{ secrets.GITEA_TOKEN }}