Merge pull request #2453 from geminicaprograms/patch-1

fix: needs `var` for Dog extends abstract class

Author: julienrf

_overviews/scala3-book/domain-modeling-tools.md

@@ -415,7 +415,7 @@ abstract class Pet(name: String):
   def age: Int
   override def toString = s"My name is $name, I say $greeting, and I’m $age"
 
-class Dog(name: String, age: Int) extends Pet(name):
+class Dog(name: String, var age: Int) extends Pet(name):
   val greeting = "Woof"
 
 val d = Dog("Fido", 1)