Augment FirebaseOptions dummy during CI build

Otherwise the CI build will fail
> error • Target of URI doesn't exist: 'package:inspector_gadget/firebase_options.dart' • lib/ai/service/firebase_mixin.dart:6:8 • uri_does_not_exist
> error • Undefined name 'DefaultFirebaseOptions' • lib/ai/service/firebase_mixin.dart:11:16 • undefined_identifier