CI: drop conflicting and unused dependency on test.

Author: greenrobot-team

objectbox/example/flutter/objectbox_demo_relations/pubspec.yaml

@@ -50,7 +50,6 @@ dev_dependencies:
   # package. See that file for information about deactivating specific lint
   # rules and activating additional ones.
   flutter_lints: ^1.0.0
-  test: ^1.17.10
 
 # For information on the generic Dart part of this file, see the
 # following page: https://dart.dev/tools/pub/pubspec