Use better assertion in test

Author: mskrip

tests/test_validation.py

@@ -125,10 +125,8 @@ class Hero(SQLModel, table=True):
 
     with Session(engine) as session:
         hero = session.get(Hero, 1)
-        assert not session.dirty
-        assert not session.new
+        assert session._is_clean()
 
         Hero.model_validate(hero)
 
-        assert not session.dirty
-        assert not session.new
+        assert session._is_clean()