Fix: False-optional feature returns now str, not feature

flamapy/metamodels/pysat_metamodel/operations/pysat_false_optional_features.py

@@ -52,6 +52,6 @@ def _get_false_optional_features(self, sat_model: PySATModel) -> list[Any]:
                 assert variable is not None
                 satisfiable = self.solver.solve(assumptions=[parent_variable, -variable])
                 if not satisfiable:
-                    result.append(feature)
+                    result.append(feature.name)
         self.solver.delete()
         return result