Use GLib.List.deep_copy() to fix type-argument mismatch
src/simple-scan.vala:134.31-134.42: error: Argument 1: Cannot convert from `unowned GLib.List<weak ScanDevice>' to `unowned GLib.List<ScanDevice>'
app.set_scan_devices (devices_copy, missing_driver);
^^^^^^^^^^^^
Compilation failed: 1 error(s), 0 warning(s)