only set invalid_at when required

Author: tybug

hypothesis-python/src/hypothesis/internal/conjecture/datatree.py

@@ -1018,7 +1018,8 @@ def draw_boolean(
         self.draw_value("boolean", value, was_forced=was_forced, kwargs=kwargs)
 
     def mark_invalid(self, invalid_at: InvalidAt) -> None:
-        self.__current_node.invalid_at = invalid_at
+        if self.__current_node.transition is None:
+            self.__current_node.invalid_at = invalid_at
 
     def draw_value(
         self,