Immutability Example does not generate error

[jimwillis]

Bug Report

Attempting to replicate the Sample Code found at https://www.kcl-lang.io/docs/reference/lang/tour#schema.

1. Minimal reproduce step (Required)

schema Person:
    age: int = 1  # Immutable attribute
    _name: str = "Alice"  # Mutable attribute

    age = 10  # Error
    _name = "Bob"  # Ok

p:Person = Person{}

2. What did you expect to see? (Required)

An error message specific to Immutability

3. What did you see instead (Required)

❯ kcl person.k
p:
  age: 10

4. What is your KCL components version? (Required)

❯ kcl --version
kcl version v0.11.1