fix(curriculum): ensure setters run during object initialization (#65113)

curriculum/challenges/english/blocks/lecture-understanding-object-oriented-programming-and-encapsulation/68c128cbd77e4ba9ed671937.md

@@ -50,10 +50,12 @@ Notice how we used `_radius` instead of radius inside the class. The underscore
 
 To make a setter to create the radius, for example, you have to define another method with the same name and use `@<property_name>.setter` above it:
 
+Using `self.radius` inside `__init__` ensures the setter runs during object creation, so invalid radius values are caught immediately.
+
 ```py
 class Circle:
     def __init__(self, radius):
-        self._radius = radius
+        self.radius = radius # Calling the setter
 
     @property
     def radius(self):  # A getter to get the radius
@@ -90,7 +92,7 @@ A deleter runs custom logic when you use the del statement on a property. To cre
 ```py
 class Circle:
     def __init__(self, radius):
-        self._radius = radius
+        self.radius = radius
 
     # Getter
     @property